If you are near Sedona, visiting Montezuma’s Well is a must. No, Montezuma was never actually there, and no, it is not an actual well, but trust me, the real story is even cooler. Predecessors of the Hopi built cliff dwellings around the “well” which is actually the site of a prehistoric sinkhole.
The water in the well contains high levels of arsenic and is highly carbonated, so while you can’t drink or swim in it, it provides five endemic species (found nowhere else in the world) a home. Those species include a diatom, a springtail, a water scorpion, an amphipod and a leech. This location holds the most endemic species in any spring in the southwestern United States, and no one is quite sure how deep it is. There are a few false bottoms and “pools within a pool” in the well. If you want to read more about the exploration of the well’s bottom, read here.