This room has a plaque on the wall, if Blai wants to read it before they move on.

Hopefully it doesn't say "I prepared Explosive Runes this morning"?

It reads: "Only the fearless may proceed. Brave ones, foolish ones. Both walk not the middle road."

Well that's not very helpful but it's not exploding. His standards are low.

In the next room, the path turns east and has two bridges cross two small streams. There's a bit of ivy. On the left wall, there are some levers and a plaque. Spikes block the way to the room after that.

"Are you willing to attempt this puzzle? I will prevent you from being hurt by it."

"Why do you want me to do that, ma'am?"

"It would make you more prepared to navigate puzzles in the future."

"...my intention, assuming your hospitality is sincere, is to hide for a few weeks in the hopes that the archmages will retrieve me before the person who wants human souls to power his annihilation ritual becomes aware of me. This process will not involve puzzles."

"Ah. In that case I can lead you."

Toriel pulls on the labeled switches but not the unlabeled switch. The spikes blocking the way to the next room lower, and she leads them across.

He follows her.

Toriel leads them past a dummy and across some circuitous floor markings while not actually taking the circuitous route.

"I can draw up a calendar once we're home."

Up ahead, the room is full of water, with a bridge covered in spikes forming the only path across.

How deep and how wide, would an Air Bubble cover him walking across the bottom?

He could plausibly cross before an Air Bubble expired. The water might even be shallow enough that his head would be above water if he stood on the floor, though it's hard to say. The water is running perpendicular to his direction of travel, though, so walking might be difficult.

Also, the gaps between the bridge and the wall are in many parts narrow enough that he could keep a hand on both a non-spiky portion of the bridge and on the wall simultaneously.

"Is this a puzzle or just a navigation challenge?"

"The spikes will harmlessly sink into the floor if you follow the path matching the last room. I can lead you along it if you're comfortable with that."

"Why hasn't anyone dismantled these permanently?" he asks, falling into step behind her.

"Well, there's not a lot of people in the Ruins, and those of us who live here are used to these puzzles. In the more populated areas, the king has been working to discourage spikes."

"To prevent the construction or to encourage the disassembly?"

"I expect both, though of course it's easier to target new construction."

Toriel leads them across the bridge. Blai is not impaled.

Hooray.

They head down a long hallway.

"I worry that the people you expect to be picked up by could get stuck here."

"The... archmages."

"We have had some skilled magicians ourselves, but none of them have gotten past the barrier."