This expansion was originally available only through mail-order and is now out of print.
From the rulebook:
Pits & Traps is a Warhammer Quest supplement that allows any party of adventurers that is bold enough to add two new areas to any dungeon they explore. While the new areas are dangerous, they offer rich rewards to those brave enough, or foolhardy enough, to venture into them.
When you use the new board sections it is assumed that the builder of the dungeon has decided to protect his lair (i.e. the objective room) with an additional ante-chamber protected by some of his fiercest warriors. He has also built in a short-cut to the objective room, concealed by secret doors, which leads to another part of the dungeon closer to the exit. Obviously only a great, powerful and, above all, rich individual could afford such safe-guards, so the rewards you expect to find at the end of the dungeon are somewhat greater than they would normally be.