Guinea Pig or small rabbit corner unit. It is joiner made and painted with pet safe paint.
Width is approx. 15 inches and diagonally approx. 17 inches without the ramp, so you would need a big cage for it or to use in a run outside.
Please note: It arrived with some damage, the ramp where it slots in has a split in the wood (pic 3) and a small nick in the wood (pic 1) but probably be easily sorted if you know what you are doing. You could also if you wanted cut a hole in so a guinea pig could go underneath.