"Crater Lake National Park, Oregon"
Stack up about three Gateway Arches and you've got the depth of the United States' deepest lake.
For hundreds of thousands of years, volcanic eruptions here built up Mount Mazama. Nearly 8,000 years ago, an eruption removed so much material from the mountain's internal chamber that the mountain collapsed.
The remaining caldera, now 1,943 feet deep, is the deepest lake in the United States and the ninth deepest in the world.
The 1.1-mile hike descends 700 feet down to the lakeshore, which is the only spot where visitors can swim. It's chilly, though. The average summer surface temperature is just 55°F to 60°F (13°C to 16°C). If that's not cold enough, the average temperature below 300 feet deep is 38°F (3°C).
