In the streets to the north of Strøget is the Rundetårn, the oldest observatory in Europe. Built by Christian IV in 1642, the building forms part of a scholastic complex that also includes a university library (now an exhibition hall) and student church.
A 209m- (686ft-) long spiral ramp leads to the top of the tower 35m (115ft) above the street, from where there is a good view over the old parts of the city.