Toy Story AU

pellucidar is a vast perfectly preserved mesozoic jungle located underground

The translucent ice ceiling is supported by rocky pillars that stand as high as skyscrapers. There are waterfalls and forests of cycads that were similar to the appearance of pine cones and palm trees, which were common in the mesozoic era. The light coming down on the jungle was caused by the sun that shone through the thick layers of permafrost up above. In other words, it was as bright as day. It is also very warm, like a mild rainforest. Apparently this is where dinosaurs and other mesozoic inhabitants escaped to in order to survive the K-T event. Pellucidar's most common inhabitants are dinosaurs (from the cretaceous period), birds such as archaeopteryx have also been shown to be native here.

Pellucidar is a fictional Hollow Earth invented by Tarzan creator Edgar Rice Burroughs for a series of action adventure stories. In a notable crossover event between Burroughs' series, there is a Tarzan story in which the Ape Man travels into Pellucidar.