[Pebbles82]

Platforms like Ria has are fine- adds interesting routes and places to go. I have a rat tunnel tied to the roof which leads between two hanging sputniks so makes a roof run (and also stops them monkey barring across the roof and falling!). The main thing is to make sure they can’t fall onto anything hard or sharp from a height of more than about 20cm. So ideally you put any hard or sharp items under a shelf or on a shelf and have a good depth of substrate to cushion any blows.