"Dungeon of Mystery" is a homemade level for Commander Keen 1, created with Keen Editor. It's a challenging puzzle because there are many doors and keys, and reaching the exit requires careful thought. In theory, you may be able to solve the puzzle by looking at the map, but only if you are familiar with Keen and look very closely at the tiles...
Currently, this puzzle/maze will only run in DOS, unless somebody wants to help me convert the tiles into a Flash game like this one: Flash Keen 1. I can understand some people not wanting to download an executable file from a complete stranger on the Internet. If this bothers you, you can download Commander Keen 1 from dosgames.com, a well-known web site with free downloads and message boards, then you can download the .CK1 files from me, run a virus check, and replace the original files in your KEEN1/ directory. If you trust me, then you can simply download the zip file, unzip, and run the KEEN1.EXE file. It is worth mentioning that this puzzle was a hit with the Commander Keen online community when it was first introduced. Feel free to search the web, and you won't find bad reports of viruses, etc. If you encounter any problems getting the program to run in Windows, this is normal for old DOS games run on newer systems. You might try to download DOSbox from dosgames.com.
For a list of game controls, press [F1]. To make a stone block fall, just shoot at the lower end of the chain. LEVEL02.CK1 is the same puzzle, but without monsters. Hold down [Shift] + [Tab] to walk through level 1 and reach level 2.