The Round Tower Lookout Tower – Observatory – Exhibitions – Concerts.One of the best-known and most popular structures in Denmark, the Round Tower has been a distinctive feature of the Copenhagen skyline since 1642. The Tower once soared far above the rest of the rooftops in the city, and University astronomers studied the stars and planets from the Observatory at the top. The scholars may have forsaken the building a long time ago, but during the winter visitors are still able to gaze at the cosmos from Europe's oldest functioning observatory. The platform that runs around the outside of the Observatory affords views over the old Latin Quarter – from here, you can spot most of the city's famous buildings. The Round Tower does not have an elevator, so visitors have to climb the winding, white-washed Spiral Walk, where kids often hide in the niches, only to jump out shouting “boo!” as adults approach. Halfway up the tower is the entrance to the large and stunningly beautiful Library Hall, which now serves as a popular gallery and concert venue. It hosts several exhibitions a year, and stages concerts almost every week. Above the Library is the Bell Loft, notable for its enormous wooden beams, which were used in the reconstruction of the Tower following the great fire of Copenhagen in 1728. The Loft is also home to a small exhibition of fascinating artefacts from the Tower's history, including Christian IV's wax seal, a tin of medicine produced by Tycho Brahe, and a piece of the bomb that exploded in the Library Hall during the bombardment of Copenhagen in 1807.The Round Tower was built by Christian IV between 1637 and 1642. It was the first part of the Trinitatis Complex, which combined church, library and observatory in a single building.