Luxury Oasis for Pet Rats / Critter Nation mod by /u/acroRATics

Wheatgrass is grown in the suspended container. When the rats finish digging up seeds and eating the grass, the love to construct burrows in the soil. The tubes are interchangeable, so when things need to be cleaned or move around, they can be adjusted. acroRATics is one part of a rat-loving couple, and they highly recommend supporting Central Texas Rat Rescue.

More photos here. Full discussion here.