Moondance looks around, quietly awed. 

On the other side of the door is a large square room in unfinished grey-brown stone - or almost square, it seems slightly off in a dizzying way - with a sort of ledge around it and a knee-high railing, like a narrow balcony. One corner has a very rusty steel gate. The floor is recessed, with a circular stone hatch or trap-door made of a number of crescent-shaped 'leaves' filling nearly all of it, wide enough to fit a small house through. One of the leaves is still cracked open, showing a wedge of inky blackness. 

...The ceiling proves to contain a similar hatch, or did once. It's bulging, half-buckling, like the stone once melted, sagged, and almost but not quite started to run. Which is probably exactly what happened. The walls are also slightly distorted, not quite in line. 

Hagan and Mahdi and Fazil don't look appropriately awed at all. 

"I think it's stable so long as we don't blow things up, so let's not do that," he says, touching the wall carefully.

He's frowning. "Van, do you have a spell to check if the air in here is vital -"

"I think it's fine but - yes, just a moment..." 

He can't reach Yfandes anymore after entering the bigger room, which is sort of disconcerting although not surprising. (She is not really abled for stairs and was left behind at the surface.) 

"Air's fine. Weirdly. I think there's some sort of ventilation but I have no idea how it's still working and I can't even see the spell for it." 

"Incredible," Mahdi says. "Can you sense what's down there?"

He tries. "No. Not at all. The shields on this room are only partly still in place but that one is really well shielded. - We could try to open the hatch and see what's down there? It's not magical in itself, it shouldn't explode or anything." 

He squints at it. "All right."

Vanyel uses Fetching instead of mage-gift, on the thought that it's less likely to interact with any aged and maybe-fragile set-spells, to cautiously lift each leaf. They're hinged, with a mechanism that has some resistance in it so they stay put once they're folded back most of the way. They have eyelets at the corners which were presumably once home to ropes for reeling them back by hand. 

A pool of darkness opens below. 

"I can do light easily enough but I don't know if there's reason to be more careful than we'd be at home..."

"I think I'll do a mage-light. There could be wards against unfamiliar magic, but mage-lights are one of the most commonly used spells, it won't be warded against that."

He sends a light down into the darkness.  

There's a big spacious room below with a marble floor. And some sort of circular platform in the centre, a little bit smaller than the hatch. 

"Are we going down there?"

"I'll have a look." Vanyel uses Farsight and mage-sight - the shields have a gap now that the hatch is open, he can sense through it.

"Big round room - lots of doors, I think sixteen - they're really shielded too, looks like Work Rooms for magic. But there aren't any defensive spells. I think we can risk going down." He frowns. "Maybe one of you who's, er, physically tougher than me should go first, and I'll put shields on you too. I'm pretty sure it's safe, but - Leareth would be paranoid anyway and I think that's reasonable here." 

"I'll go."

Vanyel puts lots of magical shielding on him. 

"...Does someone have a rope?" 

"Six hundred feet," the three of them say in unison. 

"Of course you three are prepared. I don't think we need six hundred feet, it looks like maaaybe thirty." 

"Yes," says Mahdi, tossing the rope to Hagan, "but once, you see, we didn't have enough."

"I'd love to hear that story. Maybe once we're not exploring a potentially dangerous buried mage-fortress though."  

It is, indeed, about a thirty foot drop to the platform. 

When Hagan lands on it, it bobbles under his feet, like a boat on water. 

"Not the stablest ground," he reports, and looks around - what else is down here.

A huge, roughly circular room, panelled in pink-veined marble, almost empty. Four large crystal globes dangling from silver chains, evenly spaced around the ceiling-hatch. Sixteen very large, heavy-looking doors. Fifteen closed, one ajar. 

The platform, when dismounted from and investigated, proves to be floating a couple of feet in the air. 

"I think this is some kind of magical lift, though I don't know if it still works."