Reminds me of cenotes down where i am...
https://www.google.com.mx/search?q=...ved=0ahUKEwjclr6G3LbRAhUG1oMKHeLvAFMQ_AUIBigB
Cenotes are gorgeous and many of them are miles long! Considered a place of gods by the Mayan people and then they all disappeared, maybe aliens? Lol!