Swamped

Your first question is how the door is even attached. But you can't get any clue to that - whatever mechanism opens it seems to be on the other side. In fact, from this side you're not even sure air can get through.

Which makes sense if it's meant to block the water, but if the priests really are inside, they wouldn't be able to last too long without fresh air. For their sake, you hope there's some other route for air to get in.

"Could you knock it down with a spell?" you ask Marian.

"That would draw a lot of attention, but there might be something subtler I can do." She touches the door. "Lightweight."

Then she starts pushing on it, and frowns.

"It didn't work. Something's interfering. It should be substantially lighter, and easier to move. In fact, it feels like I used way more ether than I meant to."

"So I suppose more destructive magic's out, then?"

She nods.

"Yeah, there's something that messes with it. If we're forcing it down, we'll have to stick to physical strength. Which means, I suppose, that we'll have to go out and find some sort of battering ram."

"Well, before that, I have a thought," Drip interjects. "It will take but a moment to try. If the rest of you would kindly give me some space?"

You stand back, and he starts tapping on the door. In a very distinctive pattern.

"You think they'll just let us in?" Arlene asks.

"Well, how they greet us depends on if the kidnappers are there, or if there are only captured priests. Either way, they should find it strange that someone is knocking on the door when there is supposed to be a mass of water outside."

"Yeah, but what if they don't know the water's gone?" Arlene muses. "Can't investigate very easily if opening the door's going to flood the place. And if they've got some way of knowing that it's gone, they probably already know we're here, so why open the door."

She has a point. So you're probably back to the battering ram plan.

Except, surprisingly, the door opens. Nobody seems to come out, though.

Everyone exchanges glances.

"This seems a lot like a trap," you say. "So, who goes in first and springs it?"