Just thinking off the top of my head...
If you got the
WotC modules:
Heart of Nightfang Spire and
Forge of Fury that may do the trick.
Nightfang Spire is a major undead crawl, so you might need to take creative liscense with things if it doesn't fit. If it does, you'll get some nifty encounters like the vampiric gibbering mouther and the mummy with monk levels (you should have seen the looks I got when a player fired an arrow at the mummy and it promptly deflected it followed by it tumbling into the characters and a "furry of blows"

) I liked the maps.
Forge of Fury is a dwarven complex that could easily be modified to be dropped below the tower (the bottom ofthe tower in Nightfang Spire is underground caverns. This is a lower level module and will need to be modified. Once again, the maps are top notch.
Hope that helps
