-- NETHACK SPOILERS --
The endgame to Nethack is reached by taking the "up" stairs out of the Dungeons of Doom on level one, with the true Amulet of Yendor. It consists of:
Four elemental planes: Earth, Air, Fire and Water. These levels exist to provide vastly different challenges compared to the previous 50-plus dungeon levels. Earth is a big cavern consisting of several unconnected chambers. Air is a vast stretch of atmosphere, and either levitation or creative use of kicking are required to get around here, while contending with lots of the newly-deadly Air Elementals. Fire is full of lava. And as for Water... let's hope you brought along a waterproof container.
After this last comes the Astral Plane, stocked with dozens of angels, (some friendly, many not, one tame), three Horsemen of the Apocalypse (Death, Famine, Pestilence – see if you can guess where – or rather, who – is War), and three High Altars, on which one, and only one, should you sacrifice the Amulet in order to win the game.
Suffice to say, most Nethack players never get even this far.