Tomas studies the runes. "It's a magic item. I don't know what its functions are. Presumably it conjures the water."

"Conjuration, so it's not just a scaled up Decanter of Endless Water. Those are transmutation. Obviously it's strong. That's all I have beyond guesses."

"I don't know. Maybe it's creating the water or transporting it from somewhere? I'm not sure if the decanter of endless water had been invented yet in Thassilon."

"It could be called from the plane of water? A Gate there might allow water through like this does, though it's clearly not just that or the place would have been consumed by water elementals or something similar. Not particularly relevant for now."

Clap. "So! Next targets. I could send Lhín down the crack Yanor spotted, if we tie a rope to her so we can pull her back if she gets trapped. If there is something down there, she might be able to tell us, though actually reaching it ourselves would be difficult. Alternatively, we could proceed the other way on the river and see if we find ourselves reaching the other side of that flow the long way around. Opinions?"

"I say we travel downriver. I'd rather not have to squeeze through such a small space. If we don't find the other end, we can always come back for it later."

Nod. "Agreed. Downriver it is."

Back onto the raft! The boats might have worked equally well, but the raft is so convenient. Prepared spellcasting is amazing.

Yanor commands the raft down the river.

They pass by the crack in the wall and the balcony and the stone posts and down through the ravine. The river widens into a breathtaking lake. Dozens of tiny colored motes of light flit and dance in the air, illuminating this vast space. To the east, the water foams as it cascades down into a lower cavern, while to the southwest, a low beach of white sand slopes up from the shore to a single stone door set in the wall. A seven-sided stone platform sits in the middle of the lake—an artificial island whose surface sits a mere six inches above the water level. A three-foot-tall stone mooring post protrudes from each of this island’s seven points. A single glass statue of a beautiful woman stands atop this platform, one leg poised before the other as if she were preparing a running leap into the water.

Her eye catches on the beach. While they're here... "Yanor, would the beach sand suffice for your Sylvan Hideaway? I don't remember the ward scheme blocking extradimensional spaces from the inside, and blocking bags of holding would be quite inconvenient. If we can rest in here, that opens up options."

"It will work only if the sand is natural and at least five feet deep."

"I have no simple way to test whether it is natural, and I suppose whatever enchantments prevent the water from removing the sand may interfere. Ah well."

Detect Magic. Is there anything notable on the platform?

Nothing on the platform appears to be magical.

"I see no magic here, including the posts. Examine it for anything of interest, or simply leave it be?"

"Detect magic doesn't really work properly here. It's possible there's something of interest we can't see. Perhaps we should investigate it later, when we come back this way again."

"A sensible approach. How close can you safely take us to the waterfall? The source had something of interest, so perhaps this side of the water also shall."

"I should be able to get fairly close to the edge. The river moves slowly and I can point the magical current in reverse."

"Let us take some time to examine it and for Lhín to detect for any oddities, then, and afterwards to the second beach?"

Yanor commands the raft down the river.

Their magic raft glides over to the other side of the lake without issue. The sound of a waterfall grows louder and louder as they approach the edge. A great cascade is before them. The water flows down a large hole into somewhere deeper. Strange light is visible on the other side.

"I do hope there is a way to descend besides this. I have Feather Fall if we must but it would be an issue to make our way back up."

At the same time, Lhín zips off the raft and around the edge of the waterfall. Are there any interesting discontinuities or gaps in the walls? Weird fiddly bits which don't make sense? Anything at all which looks like it might be intended as an access path?

Nope! There don't seem to be any intended access paths down.

"Nothing feels off."

Oh well. "Lhín detects no interesting points. If you have all examined the area to your satisfaction, I believe our next stop is the beach?"

"It would seem so." Yanor commands the raft up the river.