The Lost City is a forgotten and destroyed metropolis filled with lava, fire, and burning traps everywhere. Mostly buried inside a volcano in a mountainous chain, the place crawls with Mole Knight's minions, as well as other hostile creatures like Blorbs, Birders, and Charflounders. Rivers of lava and flammable goo flow in the deepest chambers. Mole Knight leads his operation in the deepest and farthest chamber, past fossilized remains.
In Shovel of Hope and Plague of Shadows, exploration of the Lost City is confined to the underground levels. In Specter of Torment, topside caves and ruins are also visited. Large green mushrooms related to the goo can be found there.
In King of Cards, the Lost City is divided into three stages, which are as follows:
The Lost City sunk beneath the earth a long time ago. Mole Knight started excavating it in search of forgotten and unclaimed riches and assembled a taskforce of miners to protect the city from anyone not part of his work force. King Knight battled his way through the Lost City on his way to find and challenge the Troupple King, the second Joustus Judge. At one point, King Knight dove down a mineshaft in the city and landed in a hot tub that Mole Knight and a couple of Molers were relaxing in, destroying the hot tub. Angry about his break being interrupted, Mole Knight fought King Knight to "bring him down to earth," but was defeated.
Afterwards, Specter Knight traveled through the Lost City to recruit Mole Knight in the Order of No Quarter. Work rates then doubled under the Enchantress, with Mole Knight now excavating for her army.
Shovel Knight and Plague Knight later faced Mole Knight in the sunken metropolis, with the former seeking passage to the Tower of Fate and the latter intent on stealing Mole Knight's essence. After the defeat of the Order, Mole Knight began leading expeditions through the Lost City for the Valley's inhabitants.