A long time ago, the Altrusians have built the Lost City into the base of a mountain in a region of the Land of the Lost. Now, it is their descendants the Sleestaks who live in it, although the city is partly abandoned. The city consists mostly of an underground tunnel complex and contains several important places, such as the Library of Skulls, the fog-filled pit called the "Hole of No Return" within which lives the Sleestak God, and the Nursery where the eggs are kept.
On the outside, the Lost City consists of a huge plaza with an arched entrance, crumbling rectangular pillars, and three tunnel entrances set into a mountainside. Big Alice spends most of his time on the plaza and protects the city from trespassers.
The Sleestaks don't tolerate intruders and attack anyone who penetrates into the Lost City, especially the Marshalls.