There’s a gaping hole in the ocean floor so deep that scientists have yet to detect its end.

The ‘bottomless’ abyss takes the lead as the world’s deepest blue hole – beating the Dragon Hole of the south China Sea which bottoms out at 301 meters (988 feet) below sea level.

The Taam Ja’ blue hole off the southeast coast of Mexico is more than 100 meters deeper than that. From above, the 150-meter-diameter chasm looks like the pupil of an eye, with a surrounding cerulean seabed for an iris.

But here’s the catch: This hole is so deep that not even sound, which usually travels so well in water, can bounce off its bottom. Taam Ja’ swallows the echoes of high-frequency acoustic waves before they can penetrate more than 274 meters deep.

The Yucatan is famous for its Swiss cheese-like geology, hosting an impressive 10,000 freshwater-filled sinkholes, or cenotes, and an extensive labyrinth of subterranean caves and underwater rivers. Some of these even contain precious archaeological and biological secrets that we never would have known about were it not for the driving force of sheer curiosity.

While biologists are still exploring blue holes around the world to better understand their biological community, in some cases, they have encountered whole new lifeforms.