DooM E1M2 Monday Madness

While researching teleportation and parallel universes, Aperture accidentally open a gateway to UAC's Phobos research base, which is connected to Hell itself. Fight past hell's army of Zombie turrets to the exit, then unlock all 3 gels, find out what happened to the other test subjects they sent through, and rescue any survivors. You can also try to find the 6 secret areas, and the surprise. There's a scoreboard at the end that counts your kills and secrets.

This is level 2 of the 1993 free open source shareware game DooM, by iD Software, except monsters have been replaced by turrets, and weapons, armour, and powerups have been replaced by cubes. There's also an (optional) added Gel Puzzle at the end, and some other enhancements.

Warning: Exploding barrels!

Remember, you can't portal black, dark brown, metal, computers, glass, or walls that are too small or too rough. Secret passages can't be portalled either (engine bug).

I recommend playing on Ultra Violence difficulty level. There's also Nightmare difficulty with turrets that respawn after 30 seconds, for crazy people. Can I Play Daddy is easier than the easiest level in the original game, with less turrets, better lighting, non-lethal barrels, and less gore, but is good if you just want to explore or solve the Gel Puzzle.