Altar, worship house and sacred sundial—to ancient Maya, natural wells called cenotes were all these and more. Diving in a cenote near Chichén Itzá, photographer Paul Nicklen snaps pictures of National Geographic Emerging Explorer and underwater archaeologist Guillermo de Anda as he explores an otherworld strewn with Maya offerings, from pottery to human bones. To see more NatGeo videos, visit the National Geographic YouTube channel.