Sotano de las Golondrinas – Cave of the Swallows

Caver rappelling down into the Sótano de las Golondrinas, Mexico

The largest cave shaft in the world – enormous 49 x 62 meters wide hole, 372 meters deep. Famous due to a group of green parrots who have to fly ascending in circles around the cave until they get out of it.

Black Hole of Andros

Cross section of South Andros Black Hole in south-north direction, compared with Boeing 747-400

300 m wide and up to 47 m deep round water filled sinkhole with a layer of violet jelly layer of bacteria at 18 meters depth. Microorganisms have heated up the water to 40°C.

El Zacaton sinkhole

El Zacaton and Nacimiento spring

The second deepest water-filled sinkhole in the world. The total depth of the sinkhole is 339 m, the lake is 319 m deep. On the surface of the lake, there are floating several round travertine islands. Lake is formed by volcanically heated acidic groundwater.

Sotano del Barro

Sótano del Barro, Mexico

One of the largest sinkholes of the world, 455 m deep, with 410 m direct fall. Width – 420 m, formed in Lower Cretaceous limestone.

Hoya de las Guaguas

Hoya de las Guaguas sinkhole, Mexico

Sinkhole – cave of giant size. Entrance shaft is 202 m deep, total depth 478 m, cave chamber up to 290 m tall. Thousands of swifts and parrots live in the sinkhole.

Tawi Atair sinkhole and cave

Cross section of Tawi Atair sinkhole, Oman

Enormous collapse doline, 211 m deep, up to 150 m wide, with vertical walls around. The sinkhole is full of life: numerous birds and plants. Cave lake contains endemic fish – the only freshwater fish in a 600 km radius.

Poza Seca, Sistema Zacaton

One of the unique travertine capped sinkholes in Sistema Zacatón: formerly open sinkhole has sealed itself with a limestone lid. Most likely it hides unknown life forms, not investigated.