There's a cave in France where no humans have been in 26,000 years. The walls are full of fantastic, perfectly preserved paintings of animals, ending in a chamber full of monsters 400m underground, where CO2 and radon gas concentrations provoke hallucinations.
It's called the the Chauvet-Pont-d'Arc Cave, a really weird and mysterious place. The walls contain hundreds of animals - like the typical Paleolithic horses and bisons - but some of them are not supposed to be there, like lions, panthers, rhinos and hyenas.
A few are not even supposed to exist, like weird butterflyish animals or chimerical figures half bison half woman. These may be linked to the hallucinations. The trip is such that some archeologists think that it had a ritual nature, with people transcending into a new state as they descended into the final room.
In fact, the paintings themselves are of such sophistication - some even have three-dimensional relief - that is hard to believe they were made back then. However, radiocarbon dating shows that these paintings are indeed prehistoric: A group was made around 27,000-26,000 years ago and the other at 32,000-30,000 years ago.
The cave first discovered in 1994 by three French speleologists: Eliette Brunel-Deschamps, Christian Hillaire, and Jean-Marie Chauvet. And now you can visit it too. Not in person, but in the next best thing: The great German film director Werner Herzog has made a 3D film of it, which is the only 3D film I want to watch this year (actually, amazing documentaries are probably the only movie genre that is perfect for 3D, like this or the Hubble 3D movie).