When the water of Lake Berryessa, the largest lake in California’s Napa County, is low, a strange concrete tower rises up above the lake’s surface. It’s just about the only abnormal thing you’ll see there on any given day. But when the water is high, it turns into an enormous, mesmerizing whirlpool. The concrete tower is actually a giant funnel that’s meant to act as a drain when the lake is too full. It’s only been used 26 times in the past six decades, but when it is used, visitors have a hard time looking away. That’s because it looks a giant bathtub drain, creating a hypnotizing swirl. And thanks to heavy rains in California, the ‘glory hole’ of Lake Berryessa was recently there for all to see once more. Check it out for yourself, and prepare to be amazed.