Perlan

Perlan is a prominent landmark in the Icelandic capital of Reykjavík. It is situated on the top of Öskjuhlíð hill. What was originally a cluster of hot water tanks was in 1991 converted to a building open to the public. It hosts an exhibition, a planetarium, an observation deck, and a restaurant.

In 1939, a single hot water tank was constructed on Öskjuhlíð hill in Reykjavík, where Perlan stands today. It is 61 meters above sea level, which gives enough pressure to push water up to the 10th floor of a building, 38 meters above sea level. That sufficed to supply water anywhere in Reykjavík – even to the hill where Hallgrímskirkja church stands today. In the next two decades, five more tanks rose beside the first one. They were torn down and reconstructed in the late eighties.

Wikipedia