If you opt to stay, you'll discover a dark dog the size of a bear in the center of the room. It's chained to a massive iron lever, partially buried by already fallen sediment, but you can't tell if it's the result of a partially engaged trap, mere time, or a combination of the two. The dog is too quick to engage closely, so if you're journeying alone, you're out of luck; but if you have a partner, you may be able to distract it. Choose your fastest party member to focus on the dog and least clumsy to go for the lever, or you both shall fall.
Journeying alone - OR - With a party