A burrow is a hole or tunnel excavated into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion.
Many animals build their home by digging a cave into the ground. Some just cover themselves with earth or sand, while others construct caves or even labyrinthic cave systems. But as most animals are much smaller than humans and the caves are thus not accessible, they are not considered caves.
Animals dug caves in available rock and earth, so burrows are found in rock which is not suitable for natural caves. Quite common is earth, clay, or soft sandstone. They may be recognized as burrows by claw marks on the roof and the lateral walls. Also their structure is specific, depending on the responsible animal. The south american Sloth tunnels are are long and sinuous, and have a circular section. And they are quite huge, with a diameter of upt to 2m.
During the Ice Age there were numerous giant mammals roaming the lands. Mastodons, saber-toothed cats, Toxodon were quite huge, but were not equipped for digging. But two species of Ice Age animals were digging burrows, giant armadillos and giant ground sloths. Today's armadillos are expert diggers, with powerful arms and large claws. The largest living species creates burrows less than half a metre (1.5 feet) across. South America was home to armoured giants like Holmesina and Pampatherium, which were several times larger than any of their modern cousins. Even bigger was the extinct gigantic sloth which lived in southern Brazil and in Argentina. Megatherium and Eremotherium could grow bigger than a modern rhino.
More than 1,500 palaeoburrows were explored during the last years across southern Brazil and Argentina. As those Ice Age giants died out 10,000 years ago, the caves are at least that old. But it is impossible to determine their exact age. It's still unknown, why they're so common around southern Brazil but not farther north. And of course there is the question what the animals were doing inside, or what for and how long they were using them.
As far as we know none such burrow is open to the public so far. But one is open for groups and another one is considered an artificial cave dug by indians, and it is only our opinion that its actually a burrow.