No need to be alarmed, this is just an extremely fascinating infrastructural feature -- which also happens to look very beautiful under the right circumstances. The Ladybower Reservoir is located in Derbyshire, England where it provides drinking water and hydroelectricity to the region. But it's most famous for its dam -- rather, it's known for a particular feature of that dam which attracts tourists and photographers worldwide.
Photo by 19andy76
While most dams are designed with spillovers that simply allow extra water to fall over the top of the dam like a waterfall, this reservoir has what's called "bellmouth" overflows. These two 24m diameter drains help to funnel the water into valves below. These are also called the "plugholes" by locals, who liken them to what you might find in a bathtubs.
The plugholes are only very rarely overwhelmed by water -- in fact, it takes quite a bit of rain to get things flowing (there was even a path you could use to walk around the plugholes, until recently). A recent spate of storms and extremely warm weather in the UK brought almost flood-level conditions to the area, and this week the Great Wet Sarlaac was back in action.
Photo by Paul Rowlett
Even when it's not churning with rising waters, I think you can admit that it still looks pretty dam cool.
Get it? "Dam"?