If Marlo thought there was treasure out there, then there's treasure. Marlo the Thief, well known for his quick dagger and his amulet of greed, could sniff out the loot in a beggar's second-best rag bin. But wherever he went, he hasn't come back. Normally, that would be the end of the story, but armed with a crude map and a potion of find object, you should have no problem figuring out what happened to good 'ol Marlo.
When you try to climb down into the Sacrifice Pit, roll 2d6 plus your DEX modifier to armor class.
On a 10+, you descend safely to the first level
On a 7+, there's a complication. If you're not using a rope, thief skills, or other climbing apparatus, you're now plummeting towards the stalactite-filled lower pool. If you are, you get into trouble. The rope if fraying, or the wall is slippery, or the intense winds in the pit are making it hard to navigate. Deal with the danger, or plummet to the floor.
On a 6-, you're plummeting.