Vinny sees a pond of blood about 150 feet in diameter. Faint large red crystals pierce its surface in several areas. This is where the blood poured into from above when they opened the secret door draining the blood pool.
To one side is the tunnel like entrance to what looks to be some sort of temple. A 50 foot wide “pier” juts 40 feet out into the blood pond. 6 Carved columns that look to have once supported a roof of some sort, now long gone, stick up like fingers from the “pier”
The “pier” leads into a 30 foot high tunnel, from which a brighter red glow spills forth. The columns continue inside to the roof of the carved tunnel. Vinny rappels to the pier. He notices that a 2 foot wide channel is cut into the floor so the blood can flow into the tunnel from the pond. He also notices a entrance on the other side of the pond, most likely where the winding passage from above terminates.
Vinny uses his grapple and rope very expertly (nat. 20) to get across to the smaller cave opening w/o having to trod through the blood pond. Climbing into the tunnel on the other side he is able to move upward to a door. Moving a spring loaded bar it opens. The rest of the party is on the other side of this one way door, camouflaged to look like the rock wall on the other side