By Tina Barrett
Walkthrough written by Staticon and downloaded from Tina's site:

You start the level dropping into a cave. From here, locate a small entrance into a water tunnel and swim until you can see a small cavern. Here you will find a 'gem' key and some flares.
Make your way back to where you started, and then find your way through the cave until you come into the first part of the castle. Find a shotgun and ammo.
Jump, grab and pull up into some steps and walk to the top of the stair. Locate the 'gem' keyhole and place the 'gem'. A door will open to your left and a skeleton will run toward you. Use the shotgun to make the skeleton fall into the lava. Take a look around whilst on the lower bridge and you will see a 'Star' key slightly hidden but at the moment you cannot reach it. Make your way up the slope avoiding the steam coming from the demon's mouth until you reach the upper bridge. Look down to your left to see a small medipack and retrieve it.
Jump from near the back of the small room where the medipack was, down onto the block with the bones in the lower part of the room. Then jump back onto the lower bridge.
Make your way once again, back up onto the upper bridge and walk about a quarter of the way along it, and turn around to face the door which you just came through. Now move over to the right hand side of the bridge and look down, over at the wall to see another room. Jump down from the bridge to this room where you will find a switch which, when pressed, moves a block in the lava which now allows you to get to the 'star' key on the lower level. To the right of the switch, you will see an opening and climbing bricks on the wall. Climb up about two thirds of the way and do a back flip onto a ledge behind you. There you will find a crowbar, which is needed to retrieve the 'star' key on the lower level. Drop down from here back into the passage with the slope and make your way back down to the lower level and retrieve the 'star' key.
Go back up the slope back to the upper bridge and walk to the centre of the upper bridge, and look right. Jump and grab and pull up into a small room. Watch out for the hole in the floor. Retrieve the 'holy prayer' from the pedestal, drop through the hole and then make your way back up the slope to the upper bridge for the last time and cross the bridge to enter the spiral staircase.

Follow the stairway to the bottom. You will notice a closed door, so go back to the bottom of the stairway to find a small opening under the stair. Crawl into the low tunnel until you get to the bottom of the ramp. Stand up and face the wood wall, and climb up into the room of lost souls. Press the switch, this opens the door at the bottom of the stairway. There is no need to continue along the low tunnel as it does not lead anywhere that is needed, however feel free to check it out, You can get a glimpse of another room from here. Crawl back to the bottom of the stairs and go through the now open door.

You are now faced with a long catacomb, in which there are pits, some of which have lava in. Two skeletons start to run toward you. The best thing to do here is to shoot the skeletons into one of the pits or they will be hounding you for some time.
When you have taken care of the skeletons, look around for a pit with spikes. Now find a tunnel with a ramp that leads upwards and walk along to the end where you will see a dragon symbol on the floor. Stepping on this will lower the spikes. On the way back to where the spikes were, look through one of the windows to see where you will be going soon. Crawl through the space where the spike were, and up into a room with a switch. Press this switch to open a door along the catacomb hall. Leave this room via the normal doorway, turn left and walk along the catacomb hall to find the opened door on the left. Enter this room and find another dragon symbol. Stepping on this raises a cage in another room, which is timed. It would be best to check out where this other room is, as you will have to climb and run to reach it before the cage goes back down. To reach this room, look over to the right hand side of the door in which you came through and you will notice a hole in that corner of the ceiling. Climb through the hole and go to the other end of the Hall of souls and drop down into another room. This is where the raising cage will be found. You will also notice a jump switch on the wall that can only be reached from a raised cage. Go back to the room with the dragon symbol on the raised surface and step onto it. The timer doesn't start until you leave it. Now climb through the hole in the ceiling after stepping on the symbol, and run as fast as you can to the other end and jump down into the room to see the raised cage. Climb onto the cage quickly before it goes back down and jump for the switch on the wall. Once activated, it will open the last door in the catacomb hall. Make your way there.

Go through the doorway and you will see a red carpet laid out for you, however this carpet does not welcome you. Run forward and jump up to one of the sides as soon as you can or a rolling ball could squash you.

If you do make it into the next room, you will need to jump a few platforms over a lava pit into a small chapel type room There are some pickups here but this room can be visited from a different entrance shortly. If you go this way, you will need to explore for yourself for a while as this walkthrough assumes that you have avoided the ball by jumping onto one of the platforms at the side of the carpeted passage.

When the ball comes to a halt in the doorway, another door will open revealing a secret passage. Walk along the passage and into a large 'L' shape room that has parts of the floor missing. There is a skeleton wandering about in here so beware.

Jump to the platform ahead and to the left and climb over the box. On the other side, to your left, you will see a crawlspace with some valuable shotgun ammo inside. Collect this, then return to the platform and do a running jump straight ahead and slightly to the right to a platform with a vase on it. Climb the projecting platform to your right to collect a small medipack then drop back down to the platform you came from.

It's now time to get wet. Jump or dive from this platform into the water. Swim into the other half of the room. At the far end, you will find a keyhole for the Key Star. Use it, then turn and prepare to defend yourself from a golden Harpie.
Dive back into the water and swim back into the first half of the room and swim to the pole. Climb and back-flip onto the ledge. This is the ledge with a vase on it (unless you blasted the vase). Ahead, is another ledge with a large box on it, in the corner on the same wall as the pole. Do a running jump and grab. Pull yourself up onto this platform and turn left. Another running jump should land you on a platform in the archway that joins the two halves of the room. From here, a short jump gets you to the entrance of the Chess Room.
Feel free to explore before entering the next room but watch out for hidden dangers.

In the entrance to the Chess Room, you will find a grenade launcher and some ammo. Pick this up and drop into the room. Run straight ahead until you come to a door, which will open, as you approach. This leads into a small chapel. There are some useful pickups in here but watch out for the sneaky skeleton who may appear. If you explore this room you will see, through the door at the opposite end of the room, the lava pit room with its other door blocked by a large golden ball. Also, one of the windows leads through a short passage back to the 'L' shaped water room.

Go back to the chess room. In the diagonally opposite corner, you will see a closed door and to open it, we need to do a bit of pushing. The floor of this room is laid out like a chessboard and there is one moveable block stood upon it. The clue as to how to move the block is in the floor decoration. They are all marked with chess Knights. Most of these are facing right but a few face in the opposite direction and are laid out in legal knight move formation. Push the block over these left facing tiles and, one by one, the closed doors will open.

When the third door has opened, run along the corridor and up the ramp. This will bring us into the church, which is full of spikes, which can be seen through the large gate to your left. Follow the passage to the left and run to the far end. A skeleton will attack in this corridor but he is easily disposed of with a grenade.
At the end of the passage, go through the opening on the left and place the Holy Prayer on the altar. The evil entity that controls this place is none too pleased.
Head back the way you came and climb the gate. From the top, you will see a series of ropes, which we have to swing across to reach a platform at the far end of the church. You will need to do a running jump and grab to get to the first rope. The other ropes are quite close to each other so don't swing too high before jumping. When on the last rope, swing as high as possible before jumping and grabbing. There is a door from this platform that was opened by placing the Holy Prayer. Go through this door and along the short corridor to the Battlements.

Run down the steps. A knight and some skeletons will appear. Dispose of the skeletons and jump onto the battlements. Make your way along the wall and follow it to the left. At the end, drop off the wall but hang on, there is a wall switch here, which you may as well operate now. Once you have dropped to the ground, turn right round. A little to the right, there is an opening into a cave. Go in here and head toward the stone columns with question marks on them. Beware of the pit of spikes. Do a running jump to the column immediately ahead and activate the jump switch. Do a running jump to the column just to the left of the door you came in by and activate the jump switch. Turn to the left and do another running jump to a third jump switch.
You will now need to do a running jump into the alcove in the cave wall behind the column you are currently stood on. Once in, head to the end of the cave where you will find a small medipack. From here, slide down toward the lever switch on the last column. Do not jump yet. Firstly, continue across the end on the cave and jump over to the ledge in the corner. Drop off the edge and shimmy round the corner. Climb back up and you will find, in a small hollow, some shotgun ammo on a dragon-patterned floor. Climbing in here stops the flames by the lever switch.

Do a running jump to the lever switch and activate it. The cage on the central pillar now drops. Jump and grab, then climb onto this pillar and take the Key Gem from its pedestal. The evil entity is most displeased that you have got this far and starts an earthquake in his anger. He also releases another Golden Harpie to attack you.

Escape from the cave and make your way back to the battlements of the castle. Climb back onto the wall and you will see that two more skeletons have joined the knight. Dispose of these. Look about until you see a boarded up doorway at the top of some wooden steps. You must lure the Knight up here. Only he can smash the boards with his sword. Run into this room and down the steps. There is a keyhole for the Key Gem here, which you must now use. Run back out of this room, down the exterior steps and back to the main area. In the corner are some boxes and a raised cage. Climb but beware, there is another Harpie on the loose. From the top of the cage, you can jump, grab and climb onto a ledge. From here, you can see a rope hanging which, if you wish to use it, will lead to a secret pickup. Otherwise, there is a window in the tower, which can be reached from here. This is the way to progress. Do a running jump and grab to get into this window. Inside, jump to the dragon platform and from there, to the open doorway in the wall.

You should now be at the top of a steep ramp. Slide down into The Maze. Search the maze for a jump switch. You may notice a crawlspace with a lava pit in it. You cannot get past this until the lever has been pulled. When you find the lever, concealed above a door arch, activate it and find your way back to this crawl space.

There is now a convenient grating above the lava, which will permit you to cross in safety. Once on the other side, continue searching the maze for a lever switch, which must be activated to allow you to escape from the maze.
Once the switch has been thrown, continue searching until you come to a room with a sloping floor and a grating in the middle. Go to the exit on the other side of this room and follow the passage to a pole, which you must climb. At the top is another passage but this one has steam and fire jets to dodge. Make your way through this passage into a room with Crocodiles in. Dispose of as many as possible before diving into the water.

In the water, is a submerged passage, which you must swim along. There are three rooms down here connected by passages. As you enter the first, a cage rises and blocks a hole in the roof. Keep going. The second room contains a large medipack and the third room has the Scarab, which is the object of your quest. Picking up the Scarab causes the cage to drop in the first room, so you must now swim back the way you came and then swim up into the hole in the roof. This leads into a short passage terminated with a rock wall and another shaft. Swim up this shaft, and you emerge in a small cavern with one exit. Drop into the passage and enter the room carefully as some spikes will rise and skewer the unwary.

We now have a long climb ahead of us. There is a ledge to the right as we enter. Climb onto this. Running jump to the platform diagonally opposite. Turn slightly left and jump up to the ledge ahead. Another running jump to the diagonally opposite corner. Do not grab or you will not make it. Turn left, jump, grab and climb to the next ledge. Turn left and do the same again. Left, jump, grab and climb once more. Now it's another death defying running jump diagonally across the room. Turn left and walk to the edge of the platform. Jump up, grab and climb. Walk forwards then repeat the last actions. Walk to the edge and you should see a door in the wall. Jump to this door, grab and pull yourself up. You are now at the top.

Enter the passage ahead and follow it to the top of another ramp. Slide down this ramp and jump at the end of it. You are now in a room with four pillars with sloping tops that you slide down. To escape from this room, you must drop off of these slides into the water below. There are Crocodiles in the water and one platform with a pole, which you can swim to and attempt to dispose of the Crocs. Below this platform, in the water, is a hidden doorway. Swim through the lost souls and you will find yourself in a tunnel, which slopes down then up a shaft into a small room with a lever switch in it. This switch re-aligns the sliding blocks to allow you to reach the door. Activate the switch. When you throw the switch, a flame will activate. You will have to run through it so check your health is up enough to let you reach the water. Swim back to the column room and climb onto the platform with the pole. Climb the pole and jump onto the sliding columns. I have found that you need to be right up by the roof before jumping or else you will miss the column and drop back into the water. Slide and jump on each of the columns. The last one will let you jump to the exit door. Just down this passageway, there are some grenades to pick up.

Follow this dark passage to where it opens into a crypt-like room. Be prepared. Skeletons and Harpies will attack you. Having disposed of these enemies, exploration of this room will reveal a number of coffin-like boxes, a closed door and keyhole and, below an effigy of your unseen foe, a gem surrounded by fire. To get to this gem, we need to shatter the bones of the evil entity. These can be found on top of a rock with demonic carvings on and above it. The bones are red and you must shoot at them until they shatter.

The fire will go out once the bones are destroyed and you may now retrieve the gem, which you must use in the keyhole by the closed door. Once the door opens, you can make your escape from Castle Doomsday.