In the summer of 1894, a hapless fortune seeker scoured the slopes of what is now Ice Mountain with a divining rod, intent on finding the fabulous silver deposits he (for whatever reason) believed were buried underneath. When the magical stick finally showed him the spot, he set to digging. However, in a departure from how this type of scenario typically plays out, he did not come up empty-handed.

Instead, he struck a deep subterranean shaft bizarrely full of ice.

The Coudersport Ice Mine is an intriguing and puzzling geological anomaly. In the spring, as the rest of the Northern Hemisphere thaws, ice begins to form in this 40-foot-deep cave, increasing in volume as the temperature outside gets hotter and hotter; you can visit on a hot summer day, stand outside of the mine, and feel a cool breeze from the ice that forms inside the rocks. Then, in the fall, the ice starts to melt, dwindling down to nothing over the course of the winter, only to begin the cycle again once the chill finally starts to leave the air.

The dynamics that drive this counterintuitive process are not yet fully understood, but the current prevailing theory states that fissures in the mountain overhead draw in cold air during the winter, then expel it in the summer. Thanks to the serendipitous pattern of these fissures, the expulsion process channels all of the cold winter air into the Coudersport Ice Mine, where the superchilled environment draws moisture from the humid outside air to form ice.

As the previous winter’s air flows into the cave, the fissures fill with warm summer air which will subsequently be pushed into the cave in the winter, melting the ice in the process. There are other ice caves like this — particularly in other geologically similar places in Pennsylvania was well as West Virginia and New York — but Coudersport Ice Mine is the largest such cave east of the Mississippi.

The cave was actually used to store food and other materials shortly after its discover, but has simply been a curious local attraction since the early 20th century. Today, a viewing platform at the top of the Ice Mine allows visitors to peer down into the odd icy shaft below. The temperature is continually tracked throughout the year, and geologists are currently studying the mine to learn more about the natural phenomena at work in the cave.