Behavior of Gilamonsters
Gilamonsters are very inactive lizards, which primarily are active from dusk to dawn, and in shorter periods during the daytime, where they come out to get some sun. The majority of the day is spend in natural hides, such as rabit holes, underground tunnels, or under big rocks.
On of the reasons for this underground behavior, is that the lizards do not tolerate to high temperatures over longer periods. Furthermore the lizards like it to be a bit more moist than it is on the surface, and this is possible to find under the ground.
These aspechts are important to think of when you are decorating a terrarium for gilamonsters. They need a hotspot where they can get warm, they need a cool end and they need the possibility to find a moist area. The moist area is made with a humid hide.
Beside the above mentioned, gilas like to dig a lot so the need enough bottom substrate to dig in it, as this is a natural part of their behavior.