Nethack is a single-player dungeon exploration game. The emphasis is on discovering the detail of the dungeon. Each game presents a different landscape - the random number generator provides an essentially unlimited number of variations of the dungeon and its denizens to be discovered by the player in one of a number of characters: you can pick your race, your role, and your gender.
Nethack is graphical by default. To toggle zoom, press Alt-Enter. To use the text map, press the F5 key.
Nethack saved games are stored in /c/nethack.
You can find more information about nethack at nethack.org