Located at the Monticello Dam at Lake Berryessa in Northern California, this gigantic drain acts as the lake's spillway.
Technically known as the Morning Glory Spillway it is locally, somewhat more colorfully, known as "The Glory Hole." When the dam reaches capacity, the spillway swallows water at a rate of 48,800 cubic feet per second, emptying about 700 feet away through an enormous concrete pipe. Not a safe place to swim, in 1997, a UC Davis graduate student was pulled into the glory hole while swimming and drowned.
The dam and spillway were constructed between 1953 and 1957, choking off Putah Creek and drowning the remains of the town of Monticello. At very low water levels, the foundations of the town can be seen in parts of the lake. The outside diameter is 72 feet, slowly narrowing to 28 feet at the exit. While this is the largest drain of its kind, there are other Glory Hole spillways around the world, including one in Whiskeytown Lake, and in Northern California.
Daring skateboarders have been known to use the exit of the spillway as a ramp in the dry season.
You can see the Glory Hole from the lake, but it is cordoned off from boaters and swimmers for safety reasons.