Esh'i'ear - The Eye in the Dark

Below the Broken Tooth, several days journey from where the dwarves are set up is an underground tower made of magically-infused ice. It sits suspended six ice columns one hundred feet over an underground lake.
To the east is a cavern exit that leads to the ruins of a drow city.
To the south is a cavern exit that leads to the snow elven entrance (no longer hidden thanks to the broken tooth. It also has a secret passage that leads to the dwarven realms. Only the higher ranked dwarven military new of the passage and it was off limits to most.)
The snow elves used this encampement to watch the one known exit out of the dark elf city.   Today, the tower and the six supports are home to a colony of spiders. The secret entrance to the dwarves is no longer a secret thanks to burrowing creatures.   The tower itself is guarded by a massive queen spider that obtains tribute from the other spiders in the colony.