Købmagergade 52A,
1150 Copenhagen,


One of the most popular structures in DK

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.

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.
The spiral walk is unique in European architecture. The 209 m long spiral ramp winds itself 7,5 times round the hollow core of the tower, forming the only connection between the individual parts of the building complex.

The Library was once the home of the entire University book collection. Situated halfway up the Round Tower, the Library opened in 1657. It housed approximately 10,000 books, which had previously been spread around old university buildings in the city.
At one end of the hall was an exhibition of Old Norse artefacts, which would grow and become known as the National Museum.
By 1861, the book collection had grown so big that it was moved to the new premises on Fiolstræde.
The old Library was later used as a studio by theatre-painter Carl Lund, and as a depot for the Zoological Museum.
The Library was restored in 1987 and now serves as a popular gallery and concert venue.


The planetarium in the Round Tower is a three-dimensional model of the Solar System with the Sun at the centre, orbited by the six innermost planets. Copied from Bayer’s early-17th-century work, the background depicts the starry sky of the North. It was mounted in 1928 as a replacement for the original 1740 model.
The original planetarium showed both the Copernican system, with the Earth orbiting around the Sun, and Tycho Brahe’s divergent system, with the Earth at its centre.
The planetarium was not installed until 1697, but it was built by Ole Rømer, astronomy professor and head of the Round Tower observatory, as early as the 1670s.

Used by the University of Copenhagen until 1861, the Round Tower is Europe’s oldest functioning astronomy observatory. It is now regularly used by amateur astronomers and others who wish to explore the skies.
Astronomy was an important science in 17th-century Europe, and Denmark’s Tycho Brahe was one of its leading figures. It was almost certainly due to Brahe’s influence that the Round Tower was built as a university observatory in 1642. Unfortunately, he died in 1601, so did not live to see it. His close colleague, astronomy professor Longomontanus, was the first head of the new stargazing tower.

From the platform, 34.8 m above the street, the visitor has a magnificent view of the old part of Copenhagen. Along the edge of the platform runs a beautiful wrought-iron lattice made in 1643 by Kaspar Fincke, Court Artist in metalwork. In the latticework, Christian IV’s monogram and the letters RFP are seen; these letters represent the King’s motto: Regna Firmat Pietas – Piety strengthens the Realms.