A while ago, I've found one secret in the Temple of Baa in Castle Ironfist.
If you open the secret door behind the altar in the large altar room, go to the right, then turn right again and before the last turn right, click on the last or the one before torch on the right wall. There you will find 5000 gold, which will help to every lower lvl party.
On the attached screenshot you'll find the torches I am talking about (but the screen is taken from the other side of the corridor, so the torches are on the left wall in this pic).
Hope it helps someone.

Yeah, i stumbled upon this one not long ago, it was a very nice surprise for my noobs party ! ^_^

That's the only real reason to do the whole dungeon ;)
Okay - and I love to annihilate skeletons: cool sound when they collapse!