Cenote Angelita

A vertical shaft 17 km south of Tulum that drops past a 30 m hydrogen sulfide layer to a 60 m floor. The dive begins with a black water descent through clear freshwater, then at ~27 m a dense sulfide cloud appears as a milky river — divers see the crowns of long dead trees and tangled branches rising up through it like a drowned forest. Punch down through the 3 m murk and the lower halocline opens into amber, anoxic salt water that smells like sulfur even through the regulator. Locals call it "The Nightmare." Sealed cenote with no cave overhead — open vertical shaft only, but the depth and stratified visibility make it a Level 3 dive in the Quintana Roo grading system.