"No visible magic here, so hopefully no bound demons yet. If we wish to stop for preparations, I recommend also the raft spell. Tomas, your eye for traps which are not magical? A trap here would be strange if this door was intended to be used, but if we are pausing anyway it seems worth the time."

"As far as I can tell, the door is not trapped."

Yanor sits down and starts meditating.

Once Yanor is done with his preparations, they can stand back and Lhín will spend some time pushing buttons, then.

Most of the buttons don't do anything. When Lhín pushes the central one, the doors silently swing open. Thassilonian writing is revealed at top of the doorframe.

Yanor translates for them. "It says 'Ayandamahla is bound to the Light for all ages'. I think."

"It's certainly still lit. Perhaps she is."

What is on the other side of the door?

A sloping sandy beach extends down from smooth stone walls here to the edge of a slowly flowing river. They seem to have been transported into a wide ravine. The moon hangs in the open sky at twilight. A salty wind blows from the sea.

Two skiffs formed from solid smoke are moored to four-foot-tall stone posts protruding from the sand near the river’s edge. Each boat is relatively wide and has room to seat five or six.

That is an incredibly impressive illusion — Lhín says she was probably an enchantment runelord, but it seems that doesn't preclude being remarkable at the other schools of magic as well.

...is it an illusion? Detect Magic. Any sign of a doorway between realities like Morgethai had?

"Trust the magic boats, or rely on Yanor's Flotsam Vessel? Personally I prefer the spell we understand, but there could be defenses the intended transport will bypass."

This space is full of a strong transmutation aura that wasn't present in the previous rooms. The skiffs and posts possess moderate conjuration auras.

Tomas walks down the beach. "Both the boats and posts are magical. I'm not sure of their specific effects."

Transmutation? That's confusing. Matter manipulation like Mage Hand, perhaps. And no illusion, even stranger.

"There's some sort of..." She quirks her head a little, focuses again. "Transmutation on this space? I've not heard of anything like this from transmutation. To what purpose would a transmutation be set, though? And that's the only spell I see here, so it must be preserving the sky as well unless something is hidden."

Let someone else suggest matter reshaping if that's a reasonable idea. A confident and inaccurate proposal here would hurt her more than an accurate idea would help, and it's only a guess.

Yanor studies the aura for a few moments. "I have no idea what the transmutation does. Maybe it generates the wind? Permanent control winds? Though that would be moderate and it's not a wizard spell."

"Do you know whether Control Weather is sixth or seventh circle? I believe it is one of the two, and a permanent version could have that aura."

"Control weather is seventh circle. I'm not sure if it works underground and I'm certain that making it permanent is a lost art, if it was ever possible."

"And I suppose it wouldn't explain the sky, even if it was that. Do you see a Permanency worked in there? If there is one I don't know I would catch it behind all the other Permanencies in the area, but without one a Control Weather seems quite unlikely. Anyway, perhaps a new spell. If so I am sure there will be some interested buyer, so give me a moment to copy down what I can see of the structure before we move on."

She pulls some paper out of her pack and starts drawing out what she can see of the spell. A wizard with this won't be able to scribe the spell themselves, but it should be a substantial step in the right direction for anyone trying to recreate it. Who happens to have seventh, eighth, or possibly ninth-circle transmutation slots to do the experimentation in and wants to spend those on recreating a strange runelord spell of mysterious and unclear effect. Perhaps there won't be any purchasers.

"I don't think there's another permanency." He will wait for her to finish the drawing the spell.  

"Surely someone wants a new permanent seventh-circle transmutation, in that case."

Once she's done with her drawings, she tucks them away and gets back to the question at hand. Can she tell anything about the skiffs?

The skiffs are a magical effect generated by the stone posts. The stone posts are magic items. She can't identify exactly what they do.

Oh well. "Yanor, perhaps you will have more luck with the posts than either I or Tomas." She sounds somewhat resigned to not knowing what these will do, but an extra set of eyes shouldn't hurt.

Yanor studies the stone posts. "I'm not sure what they do. Presumably they conjure the boats."

"Agreed, but I know not what the boats do. Does anyone feel inclined to test them out? A Flotsam Vessel should be sufficient for our propulsion needs, and I would prefer it to millenia-old magic items we can't identify." A note of finality to that last bit. If someone really wants to try the smoke boats, fine, but the safe way seems... safer.

"Very well." He takes a minute to conjure the raft and climbs on board.