"Where is Azlantl?"

"It was destroyed eight thousand years ago. There are some barrier islands where the continent used to be, other side of the world from here."

"...Oh. How? What destroyed an entire continent?" 

"Someone pulled a moon out of orbit to destroy an enemy they were at war with. Would've destroyed the whole world, but some gods died, trying to lessen the impact."

"Or so they tell us."

Vanyel spends thirty seconds being speechless and horrified. 

“Wow,” he says finally. “That’s even worse than our Cataclysm. Anyway, er, I’ll try to disable the constructs.”

Are there any snippable-looking points in their magical structure? Using Farsight and mage-sight to orient, he can put up a barrier around the first he tries, just in case he’s wrong and it does go boom.

Their magical structure seems to be made of somewhat firmer stuff than Mahdi's spells; snipping at it seems to temporarily alter it but the magic rushes back in once he stops.

What if he does it harder, trying to rip out the center?

It takes substantially more effort but he can absolutely do that! Then this construct is just a weird stone statue. It courteously does not explode.

Well, Vanyel isn’t exactly limited by power, so he’ll do all of them (not bothering with the shield after the first, unless he comes across one that’s significantly different.)

They all seem to be of the same type and shortly they are all gone.

Then he will carefully start poking at the spells on the door, again looking for traps. (And shielding the group of them just in case.) 

Several of the spells on the door are traps that are intended to paralyze and poison and stun the magic away from people who open the door. Several of the other ones are set up to alert people if anyone is disrupted.

He's glad to have checked! Presumably the alerting-people spells no longer have anyone to alert, but he'll try to trace where they go anyway and snip them upstream, when he gets to them.

Probably if he maintains really really thorough magical shields on them, the trap spells won't get through? Just in case, he asks the others to back off out of effective range, so there'll be someone to scoop him out if he needs it, and he'll do it from the furthest distance he can and still have his mage-sight precise enough, which is about thirty paces. Can Fazil heal him from the paralysis or poison ones, if he's wrong about being able to shield them? 

"I can do everything within thirty feet any time, and a specific target at seventy feet if I have Sacred Bond up. It lasts about an hour and a half so I mostly wait until we're plausibly going into a fight. I can do it now, if you'd like."

"The paralysis one won't kill a person instantly; I'm not actually sure if it'll stop me from breathing, but even if it does, you'll have thirty seconds or a minute to get in range, so I think the thirty-foot version is fine?" 

"Sure. - I would expect them to not want to kill people breaking into their palace? Usually if people are breaking into your palace you want to ask who sent them."

"If you try to break into the Dome they kill you and Speak With Dead your corpse. Talked once to a guy who had a good enough explanation they raised him. Not apologetically, but."

"I think it should be pretty safe to try to disable the traps at thirty paces."

"I mean, I'm hoping I can shut it down without triggering the trap at all, or that if I do, my shields will get it. Just being cautious. Can everyone else, er, get back behind the last bend in the tunnel? ...Fazil, if you hear a thud, come running. Carefully." 

"You got it."

Then Vanyel will follow the structure of the spell, and try to snip or tear or crush it at a place where it looks like it should implode rather than trigger on him, if he can find such a place. 

There are a bunch of them; like the constructs they're a lot harder to permanently alter than Mahdi's spells; they can mostly be torn apart with enough force, though one of the alarm ones triggers a probably-irrelevant alarm and one of the poison ones tries to poison persons standing closer to the door than thirty paces. 

Fortunately Vanyel is being very careful. He warns the others about the alarm, they'll need to be on the alert in case it activated other defensive spells later on, and then they can open the door. 

And then they can enter the palace. The destroyed constructs are spaced evenly on the wall. The floor is a beautiful tile mosaic apparently starring a man with the head of a jackal. There are some paintings on the walls that are still intact.