As much praise as B2: The Keep on the Borderland gets, it's actually my least favorite of the four modules I've selected. That's not saying there aren't caves I really like, such as the Shine of Evil Chaos and the Ogre's and Bugbears' lairs. But there are some that just don't have much character too them and need some spicing up, the gnoll caves in particular.
Aplus at People them with Monsters wrote a fantastic reworking of the Kobold caves--another that I don't find particularly compelling. You should really check it out.
The main thing Aplus has done is added an Abandoned Mine section to the kobold lair. Within the mine is a pool, in which there is a Amphibious Kobold Mutant. The main treasure in the lair is now a bundle of copper nuggets, but not only are they copper nuggets, but copper nuggets that mutate the their possessor. Nice, hu?
Yesterday, I took the time to copy out the Caves of Chaos onto a work processor. I haven't gotten around to modifying anything, and, honestly, I don't plan on changing all that much, mostly just adding a little more character to some of less interesting caves (the gnoll and orc caves in particular).
So here's what I want to know: what have you done to make the Caves of Chaos just a little more unsettling and/or interesting?