The Altar was opened, and the treasure found! And no one actually died!
On their way to Brightstone Keep, the brave band crossed a troll bridge and managed to slay a juvenile Skrag, whose parents were conspicuously (and fortunately) absent. Maybe it was a juvenile delinquent?
At the keep itself they met a friendly competing party who were after the same thing. However, their rivals proved noble and the cleric there agreed to heal them all in exchange for them taking the first two watches. Predictably, the rival group got an early head start into the mine rather than stick around to watch over their sleeping competitors.
After making their way to the Serpent’s Temple via an unnecessarily circuitous route, they managed (barely) to survive and defeat two invisible Phantom Fungi and to solve the altar’s puzzle (which ended up being far more difficult than it was intended to be – no champion riddlers we).
5 Jeweled Chalices, 4 Silver Salvers, and 2 Gold Censers (along with one ancient stone tablet) constitute the prize.