Jacob's Well is a perennial karstic spring in the Texas Hill Country flowing from the bed of Cypress Creek, located northwest of Wimberley, Texas. The twelve foot (four meter) diameter mouth of the spring serves as a popular swimming spot for the local land owners whose properties adjoin Cypress Creek. From the opening in the creek bed, Jacob's Well cave descends vertically for about thirty feet (ten meters), then continues downward at an angle through a series of silted chambers separated by narrow restrictions, finally reaching a depth of one hundred and twenty feet (forty meters). Until the modern era, the Trinity Aquifer-fed natural artesian spring gushed water from the mouth of the cave, with a measured flow in 1924 of one hundred and seventy gallons per second (six hundred and forty liters per second) discharging six feet (two meters) into the air. The spring is the greatest source of water recharging the Edwards Aquifer.

Cave Diver, Anhumas Abyss, Bonito, Brazil: The Anhumas Abyss is an underground cavern with a crystal-clear lake below, more than 260 feet (79 m) deep. A visitor must enter through a narrow opening at the top of the chamber and rappel into the cave. Snorkeling and scuba diving in the lake reveal amazing scenery. Distinctive, conical limestone stalagmites and stalactites occupy the lake and the surrounding area, some reaching 65 feet (20 m) high. (Photo by Marcio Cabral/Nature’s Best Photography Awards 2017)

U.S. Capitol Police with guns drawn stand near a barricaded door as protesters try to break into the House Chamber at the U.S. Capitol on Wednesday, January 6, 2021, in Washington. (Photo by Andrew Harnik/AP Photo)

Aoife Ni Heochaidh enjoys the sunrise as she welcomes winter solstice at the 5000-year-old stone age passage tomb of Newgrange in the Boyne Valley, as entry inside the chamber is closed for the second year due to coronavirus disease (COVID-19) pandemic, in Newgrange, Ireland, December 21, 2021. (Photo by Clodagh Kilcoyne/Reuters)

An Orthodox activist (Right) clashes with a gay rights campaigner during a protest outside of the State Duma, Russian Parliament's lower chamber, in downtown Moscow, January 22, 2013. (Photo by Ilya Pitalev/RIA Novosti)

Mercedes Russell #21 of the Seattle Storm defends Aliyah Boston #7 of the Indiana Fever during the first quarter at Climate Pledge Arena on June 22, 2023 in Seattle, Washington. (Photo by Steph Chambers/Getty Images)

Natasha Cloud #0 and Diana Taurasi #3 of the Phoenix Mercury gather their team before the game against the Seattle Storm at Climate Pledge Arena on June 04, 2024 in Seattle, Washington. (Photo by Steph Chambers/Getty Images)