You pick up the trail once again, leaving the destroyed spiders and their allies as food for the other animals of the forest. You pass through the webbed area, and out the other side into the regular old Misty Forest, and follow the trail of the departing cultists. Though their passage was many days before, it was a large group - very large - and they took little effort to hide their tracks, so there's little difficulty here in keeping to the right path.

The ground becomes uneven. You follow the trail leading now due east, and you come upon a pool, perhaps twenty feet in diameter. The pool sits at the base of a small cliff about sixty feet high, and a waterfall cascades into the pool from above.

The tracks of the cultists enter the pool, and do not emerge.

How far from the webbed area to the pool, thereabouts?

(Did we stop to take our short rest on the way, as was the plan?)

About an hour of walking. Yes, if you wish to take a short rest after leaving the webbed area but before reaching the pool, you can do so. Feel free to roll hit dice, and an extra 1d6 from Bazavur's Song of Rest.

(I think that was the plan, yes.)

For Tangle:

1 Song of Rest: 5
1 Fighter HD: 2
2 Rogue HD: 5 

Short Rest: 14

Song of Rest: 5

Bazavur: 6 and 1

Soar short rest: 12 paladin and 3 warlock

Are there pathways around the pool to above the waterfall, or to the waterfall? Anything above the waterfall that seems notable?

"I can send Candelabra up there to take a look if that seems useful," Soar says at a whisper.

There's no pathway up to the ground above the waterfall, at least not nearby. The rocks look climbable, but there's no sign that the cultists took that route. Make a Perception check.

Soar perception -- she's looking for anything up in the rocks, anything moving, watching, hiding. Even if there aren't any trails: 5

"No need," Tangle says. Shortbow in one hand, she steals forward in the dappled light, towards the back of the pool, moving soundlessly, keeping to the trees as long as she is able. She is looking for danger, but also to confirm there is a passage behind the water. If there is, she will try to estimate if the hole is large enough for the green dragon she saw.

Stealth (w/Adv for slippers): 23 

Perception: 32 

Soar doesn't see much.

Tangle moves forward, undetected. Getting closer, you notice a strange emerald haze on the surface of the pool; it doesn't seem entirely natural. And you think you see something behind the waterfall itself, possibly an opening, possibly big enough for a dragon, but you can't say for sure from this side of the water, and you would need to swim through the pool in order to breach the fall.

Tangle looks back at the others, makes eye contact with Soar, then puts her bow on her back, and empty handed, takes a deep breath and dives into the water, swimming deep, and under the waterfall, trying to surface behind it, if possible, stealthily, if possible, near a wall (just not in the middle).

Tangle, you swim through and surface near the rocky face of the cliff and behind the waterfall; as you perhaps suspected, there is a passage, quite a wide one, leading into the cliff and down. From where you are, you cannot see very far along it.

Tangle will try to sneak up to the corner to see further down the hall.

Stealth (w/adv for boots): 29 

The passageway is wide, damp and misty, and visibility is low. You think you see a larger chamber up ahead.

What's everyone else doing as Tangle advances.  Bazavur will certainly dive in and follow, getting to the far side and clambering out as quietly as he can.

Stealth 9

Soar was hoping to wait until Tangle re-emerged, but after Bazavur jumps in, she prepares to follow, looking at Jalt with a slightly questioning expression, before a shrug. She once again asks Candelabra to find a comfortable hidden place to graze and keep an eye and ear out for anyone or anything that comes to the pool. She puts everything she's holding into the bag of holding, offering the same to Jalt and Bazavur. Then she walks around to the northeast and steps/swims in the rest of the way, around the pool, and through the waterfall.

Stealth: 5

Jalt jumps in the water and follows the rest of the party.

Stealth:  3

So, Tangle is in the lead, the rest following but hanging back?

What's the next move?

Soar pauses at the entrance by the waterfall and, silently pointing at her clanking armor and Jalt’s, indicates that Tangle can go ahead to scout for now if she likes.