This park morphs into a spectacular underwater playground at the same time every year

What looks like a lake and feels like a lake isn't necessarily always a lake. Well, at least it's not always that deep.

Welcome to Green Lake, Austria - a hiker-and-scuba-diver's dream.

This body of water literally shape-shifts throughout the seasons. During the winter, it's more like a shallow pond. But come spring, it gets deep enough to dive and swim in.

Eventually, what was once along the pond's edge becomes submerged underwater, transforming the lake into an incredible underwater oasis.