In an underwater robot entered Jacob’s Well, the footage left scientists terrified. The famous Texas spring, a seemingly calm pool of clear water, hides a deep, unexplored cave system below.

Jacob’s Well is a natural spring in Hays County, Texas, near Wimberley. It is the headwaters of Cypress Creek, where water from the Trinity Aquifer rises through an opening about 12 feet wide in the creek bed. The spring normally releases roughly 2 million gallons of water per day at a constant 68 degrees Fahrenheit.The site is a karst system, a landscape formed by limestone that dissolves over ti…