If you have some digging impliment dig down a few centimetres and compare the sub-surface temperature with that of the surface. Compare the temperature of exposed soil with the surface of leaf litter or any other mulch. Dig your fingers down into the leaf litter and feel the difference in moisture and temperature betweenthe exposed surface of the leaf litter and the protected soil underneath. There are holes and shelters that form naturally and are used opportunistically by creatures that need the shelter. The flakes of rock that form on granite surfaces are a good example.
Experienced people looking for snakes and lizards look for reptiles under such shelter.
Closer to water frogs will utilize the shelter given by rocks or logs. Small rocks half embedded in the soil surface are an interesting micro-habitat. These are the sites of many nests of small ants. The bigger ants build their own nest mounds but smaller species of ants seem to find half buried rocks an amenable place to establish a colony. This relationship is probably based on the fact that the rock acts as a heat bank and maintains a moderately warm temperature into the evening after warming up in the sunlight during the day.