Of what is a lion den made?

Lions do not build a den, they live in the open savanna. Only a female about to give birth will seek shelter away from the pride. It may be under a rocky outcrop, under fallen trees or may simply be an area of dense vegetation where she can safely give birth and raise her cubs. She will change locations frequently after giving birth so the smell does not attract predators. Once the cubs are walking and have grown some she will return with her cubs to the pride.