Avernum 3

Secret town

In the very final dungeon, players can access a secret dungeon by looking for a locked room in the southwestern quadrant with two runes. Then, after putting a pair of pants on the left rune and then stepping on the right rune, they'll be sent the "Generic Dungeon" with the most basic monsters. After beating it they'll reach an entire secret town with NPCs to talk to, including the creator of the game Jeff Vogel.