Black hole thermodynamics reveals novel features of quantum gravity in various extreme situations. I will explain that some of these features inevitably demand quantum gravity to be a drastic UV completion of general relativity. These speculations can be explored more concretely and rigorously in the holographic quantum gravity in AdS spacetime. After a general overview of this problem, I will explain some recent progress on quantum AdS black holes as well as the lessons we can learn from it about quantum gravity itself.
