Uggleviken, Stockholm, Sweden

The water reservoir at Uggleviken. It has a capacity of 18,000 m³ and was built in 1935. A unique aspect of its design is that it has no thermal insulation - calculations showed that even with an outside temperature of -25°C, the water in the reservoir was such a massive store of heat that its temperature would only drop by a few tenths of a degree. This was subsequently proven during the cold winters at the start of the 1940's, where a thin crust of ice did form but was broken up as the water level changed. (Source: Wikipedia[a])

The remains of the Ugglevik well, a trinity well that according to popular belief would have water with special healing powers. The first mention of it is from the end of the 18th century, and the water was potable until the 1970's. At present the water is not potable, and the well has been sealed. Spring water does break through to the surface, forming small streams leading down to the Ugglevik swamp.