The more natural te tank is, the better off they will be. Some kind of substrate that they can dig around in is a must. Smooth river pebbles or sand, or even a mix of both (not all at once, but part of the tank with one and .......you get the idea) Driftwood or anyplace that they can hide is also a must. However, anyplace that they can get wedged into should be avoided, like a castle turret. Personally I think that they look better with surroundings as natural as you can make them.