As it seems, we humans have a strange habit of building weird and wonderful things in the unlikeliest of places. For thousands of years, whether we’ve been building strange and impossible monuments to the gods, or immortalising the defining events of an ancient world–leaving behind signs of our civilizations has been an important part of the human condition. Some of them, however, are a little difficult to make sense of. From the temples of an ancient society, to the depths of the ocean floor–here are 15 Mysterious Monuments That Cannot BeExplained