This is the first adventure to use the Chamber Cards, a new feature that wasn't in Castle Ravenloft. Basically, the heroes have to adventure until they turn over enough tiles to reveal the Dire Chamber Entrance, and then they have to place another Dire Chamber tile on each unexplored edge along the entrance. The top card from the Chamber Deck is then flipped over to reveal what sort of monster or challenge has to be overcome in the Dire Chamber in order to win the adventure. There's a couple of different types of Chamber tiles and some special rules about them, so it pays to read that section in the rulebook before the adventure.
Anyway, we went with our standard compliment of 5 heroes and after splitting up into three groups to turn tiles over quickly, revealed the Dire Chamber Entrance. The card we chose was Stables, meaning a massive Fire Drake had to be beat. The tricky part was that we also had to place monsters on each of the other Chamber tiles, and some of those monsters ended up being Sentry monsters but we couldn't reach them because the Fire Drake blocked access--that meant that by the time the battle was over, there were more monsters on the board than I had ever seen before!
When the Fire Drake appeared, our Heroes were spread out all over, so we had to do a lot of double-moves to get them into battle position. We actually defeated the Fire Drake with both our healing surges left, but that really was pure luck: our brave cleric stood in front of the Drake for at least three rounds, and the Drake missed with every single attack due to low die rolls!
Anyway, I like the Chamber Deck idea and looking forward to seeing what else lies within in future adventures.