During the night time, these animals are active and during the daytime, they sleep.
Some examples of nocturnal animals are - hedgehogs, foxes, owls, bats, etc.
The bodies of the nocturnal animals are adapted to help them survive as they are awake during the dark.
To roam in the dark very effectively, the physical traits of these animals have evolved from time to time, like the pupils of the eyes get widened and the eyes get bigger.
A very important example of a nocturnal animal is Owl.