This unreal glow is coming from a stalagmite. It’s sitting on top of a black cardboard mask on a light box so that the only light escaping is that which is coming through the stalagmite. And yes, there is a purpose to this.
I’ve been in the department’s dark room recently, photographing stalagmites. Once they’ve been cut and polished it’s worth recording them, partly for prosperity before we start milling into them, partly so that we can make nice pretty figures for presentations and papers, and partly because it’s possible to see things in the stalagmites that would otherwise be invisible. You can pick out layers of mud or dust or other cool things that you just can’t see with normal photos.
Stalagmites tend to be rather opaque things, so as you can imagine, seeing inside them is tricky. But they’re not that opaque. So as well as taking reflected light photos, that’s the normal kind of photo where light bounces off the outside, we also take transmitted light photographs. This is where the light travels through the thing your photographing. A bit like holding a torch up right underneath your chin at Halloween to get that cool red glow!