NetHack is a single player dungeon exploration game whose emphasis is on discovering the detail of the dungeon and not simply killing everything in sight. To get started you only need to know the command ? and the command /. Press F11 to change between fullscreen/windowed.

http://apps.open-pandora.org/cgi-bin/viewapp.pl?/Game/nethack-tty-3.4.3-Os-upx.inf