I created some little hideouts for animals at my parents place.
The hideouts are a safe spot for little animals, like snails or woodlouses, who need a wet, shady spot during the dry, warm day. I placed the rocks in a way that there is a little hollow part underneath them. Big enough for snails to get under them, but small enough to protect them from predators.
They are also great observation spots, to see more of the tiny life in the garden.
A snail even laid some little eggs under the rocks.
If you're interested in building your own little animal home, I wrote a step-by-step tutorial some time ago:
How to build a home for tiny animals