The dwarven mining party leads their unlikely drow allies to the lowest level of the Undercity mines.  There, they point out a single passageway they say leads to a dwarven burial ground, where they will not go.

However they believe the sword the drow seek will be found there, and since it is not a dwarven blade they have neither love nor intentions toward it.

Hours later, the party is standing before a magical entrance that whisks them away, not to a dwarven mount, but to an Underdark turned upside down that challenges their beliefs to the core.