Map of Underdark

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Floor 2 ---- | D | ----
Tower - Floor 1 ---- ---- | U |-| O | ---- ---- Tower - Floor 2 ---- | D | ----

Key:

U - Up
D - Down
T - Tavern
1 - There are 2 exits: tower and mound. You cannot enter the tower without an item because the air is too bad to breathe. if you enter the mound, your exits will be out and tower. This tower exit is the same as the one outside the mound.
2 - There is an exit called Bridge. I forgot to check it out, but I thnk it goes nowhere, from what I heard.