Looking for a cavern adventure

[Segial]

In my current campaign the group has to infiltrate a castle recently overrun by forces of evil to take out the evil leader. The group will learn that when the castle was overrun one of the guards used a rarely used secret doorway into a network of natural caves and tunnels below the castle, and that could be the groups way in. The guard made it out alife but as a nervous mental wreck ever since. Right now I'm looking for some source material to use to setup these cavern, anyone got a suggestion for a fitting modul/adventure/scenario that I could adept?

[DiBastet]

Any cave you might need: http://donjon.bin.sh/dungeon/

Also, I won't say "dungeon magazine" because most people don't have it.

[CTrees]

Also, I won't say "dungeon magazine" because most people don't have it.

That was my feeling-there are a lot of good ones in those mags, but access isn't universal.