Blai's proprioception expands, and where he would normally be able to sense his own limbs, now he can sense the caverns around him. Here's the path he took after he fell, his own memory of its twists overlaid with the intuitive sense the spell grants him. Here's a tunnel, leading to an artificial structure that feels almost like a gash in the land; here's a lake, and across the lake a shorter tunnel leading to the same structure. If he backtracks a little bit there's something that looked like a dead end but wasn't exactly. The spell isn't giving him a map, exactly, any more than he would be able to draw a self-portrait with his eyes closed purely from his own sense of his body, but it's enough to navigate from.
The spell can't tell him the exact layout of the maze, but it can give him an intuition for its general structure. Here's the main floor; if he goes this direction, there's something-that-presumably-corresponds-to-stairs down, and more stairs down nearby it, leading to something that feels like a very shallow version of the lake he's next to. Here's the deepest part of the lake. If he starts at the main floor and goes in this other direction, there's what might be stairs or might be a tunnel, less steep than the other path downwards; it feels like it's somehow blocked, a little like a tunnel that's caved in but not exactly. If he goes in yet a third direction, there's some sort of twisty path upwards, similarly blocked, and then a little bit downwards again, and then up and up and there'd be open sky.
The streets of Kenabres are less than a hundred feet above Blai. (Vertically closer, actually, than the place that leads out to the sky.) There are divinations that would be blocked by the ground between them, but Lay of the Land is not one of them; it would hardly be very useful if it were. He can't get a great sense of specific buildings, or even specific streets, but Kenabres is built on land just as surely as a forest is. As Blai reaches outward, he can sense that that land is marred with small crevices and massive rifts, with piles of rubble large enough they practically feel like small hills, with entire blocks of houses collapsed and near-impassible. The city center is very nearly divided in two; the city walls are in pieces. Throughout the city, there's a sense of pervasive wrongness, as paths that are supposed to connect to each other are cut off by dead ends and destroyed streets.