This year’s long, harsh winter hasn’t been all bad — the prolonged cold has made incredible ice caves in Wisconsin accessible on foot for the first time in five years, Reuters reports.
Thousands of people are walking more than a mile over a frozen Lake Superior to reach the caves, which are carved out of sandstone by waves, according to Reuters. Superior is the world’s largest freshwater lake.
Polar vortexes have allowed the ice caves to remain open to visitors because the lake has stayed frozen enough to support people walking across it. People can kayak through the caves in the summer, but the caves are only accessible on foot when the lake is frozen solid.
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