A powerful eruption, which was later followed by a colossal collapse, created the deepest lake in the United States.

Crater Lake was formed by the massive volcanic eruption of Mount Mazama, probably some 7,700 years ago. The mountain has since collapsed, and rain and snow eventually filled the resulting crater. Today, it is a pristine lake almost 2,000 feet deep.

There is only one safe, and legal, way to get to the icy lake: Cleetwood Cove Trail, a 1.1-mile trail that usually opens in June and drops nearly 700 feet to the lakeshore.

It is strenuous, with an 11 per cent grade, so it’s recommended for people in good physical shape. You can swim once you get there, but you will shiver, though: Surface waters warm only to 55 to 60 degrees in summer.