Down the hall, on your left.

What could this be? Is Modhail building dungeon terrain?

Let's take another look:

 Well, that's an odd way to go about it... Why build a second level to it?

Because it's not Dungeon terrain, but a diorama backdrop:

 Once finished, this will go in the Glass Cabinet, on the shelf where all the missus' Warhammer Quest miniatures will live.  It'll add some more mood to the cabinet, really show off the minis, as well as giving me a little more space to display them on.
There's a split down the midde because that particular shelf is a double wide one. By making it in two parts, I can also use the backdrops in the narrower cabinet.

If this one goes well, I'll make a second set. Half can go behind my own Dungeoneering miniatures, with the other half used as a photo backdrop. Unless I move my own Dungeoneering kit to the double wide portion of the cabinet as well... I may need to at some point.

What I did discover while making the walls for this first corridor, is that scribing stonework is tedious. If I do build my own set of dungeon terrain, I'll really have to look into molding and casting options, or risk losing steam half way through.