Mini-Turn!
After some pleasant chatting just outside, away from prying ears, you are handed several amulets and led to waiting sharks. You put them on and then get on them, respectively, to avoid drowning and being left behind, respectively. A lean, golden-brown merfolk with a net and javelins is your "guide."
From there, it's another long ride into the depths. This particular destination is well out from shore, and the water is very, very deep here.
When you arrive, you have to be told this is the place to realize it. As far as any of you can tell, you're just on another flat section of the sea floor. Only when you start walking in the direction your guide indicates- he's not coming with you- do you begin to feel the current in the water. With visibility so poor, it's a bit longer and a much stronger pull before you can actually clearly see the edge of the sinkhole. From what you can tell, it's absolutely massive.
With little else to do, you all hurl yourselves screaming into the depths, and/or walk forward calmly until the current picks you up and swirls you down into the hole.
The journey down is rather intense, and a soft glow from the bottom is just about the only thing you can see. It intensifies as you get further down, until finally the current begins to let up and you float gently down the last several stories to the bottom.
The region you find is surprisingly lush, covered with various underwater plants and inhabited by fish, crabs, and other such creatures. More interestingly, the whole place glows softly with a bright, faintly tealish light that you can't determine the source of.
The temple still dominates the landscape, however. It's shaped somewhat like a classical temple, even being made of white stone, but you can tell there's more than one way in. A quick inspection reveals doorways set in the base of the structure at ground level, in addition to the obvious steps leading up to the central building.
Examination of your amulets reveals them to be a shark tooth on simple rope, with a rune carved onto them. Judging by the familiar pumping feeling in your throat, you would guess they're essentially permanent versions of that water breathing spell.
The starfish Tarran is carrying has undergone an interesting transformation. Its eye is now like a translucent, smooth, vividly colored gem, predominantly pinkish but with other colors in the sides.