Montezuma Castle National Monument, between Phoenix and Flagstaff, is home to a body of water that has left scientists perplexed.

The Montezuma well formed when an underground limestone cavern collapsed. Since then, millions of gallons of water have poured into the well each day, creating an oasis that has supported human and animal life for thousands of years.

While scientists know the history of the well, they have been unable to thoroughly explore its depths, despite scuba dives and probes sent down into the deep waters.