Witchaven/Level 16

At the start of the level, you will have to pull the chain to raise the platform you're on and get out. The two side chambers have some handy supplies, as well as monsters, while the wooden door is the way forward to the rest of the level. Once you drop down, pull the chain to open the bars, and grab the black key as you go through.

Continue heading north to the exit room, going to where the quiver is to trigger a passage opening, then go through it and seek out the black key door. Open the door to find the brass key, as well as a teleporter behind an illusionary wall, which you must go through.

Head down the corridor to a room with a white brick structure submerged in the water. Pulling the chain raises this into stairs. Head up and through to the overlook above the big muddy water room. Don't fall down, or you'll have to do a lot of backtracking. The way to the pentagram is on the south side, protected by a couple of doors. The first is opened by stepping on one of the brightly-lit corners of the room. The second is locked with the brass key.

The pentagram is in a nondescript-looking room, but beware! There are hidden spike traps all around it. Flight is the safest way to collect this one. Once you have it, backtrack to the exit chamber.