The dungeon map is the visual representation of all the dungeon floors that make up the dungeon in its entirety.
It can be accessed by:
Leaving the town and using the map to select what dungeon floor you want to go to.
Exiting a dungeon floor via a floor exit.
The dungeon map is used to:
Select and enter a Dungeon Floor.
Exit the dungeon to return to the town.
Viewing the stats of a dungeon floor (Like how many prisoners are left to rescue.