Initially, all of the buildings are closed off, and the only NPC living there is Elderbug. However, as more NPCs are encountered during the game, several make their way back to town and open up several buildings, including a Stag Station, two Merchants, Bretta and Confessor Jiji's (or Steel Soul Jinn in Steel Soul Mode) cave.
Sub-area: King's Pass
The Grimm Troupe's Tents
After the Knight has started the Grimm Troupe's Quests, two large tents will appear in Dirtmouth, shocking its inhabitants. The smaller tent is home to Divine, an NPC who can turn Leg Eater's Fragile Charms into unbreakable ones, for a large amount of Geo.
The larger tent contains a grand stage in which Grimm offers the Knight a charm, Grimmchild. This tent also hosts Grimm's fight. After this fight and once all flames have been collected, an area to the right of the stage opens up. At the end of a long corridor, Grimm can be found sleeping. With the Grimmchild equipped he can be dreamnailed in order to start the Nightmare King Grimm battle.
The eastern corridor of Grimm's Tent also contains a passage leading to a secret room. It can be accessed by climbing up the second arch from the left. The secret room has several inaccessible chests, the masks of the Grimmkin, and an unknown device in the middle. If a Spell is used in this room, a red barrier lights up.