Open Garry's Mod
Play Single player (clueless)
Get scared by the feeling of someone watching you.
YOU ARE BEING WATCHED.
it's a good game.
EDIT: also the game froze after killing 100 pigeons with a rocket launcher
EDIT 2: almost one week of my life wasted playing this game and it's been a blast, and i love this game. my friends make it amazing to play, and i love playing singleplayer too