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 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.

 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 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.

First big university library in Denmark

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.

Privy to the great and good

The two original privies in the Round Tower still exist – one on the top floor, the other beside the Library, halfway up the tower. Although not in use, the Library privy has been restored and re-opened. You may enter, sit yourself down and gaze up at the arched ceiling, where nicotine used to seep through the limestone in the days when it was popular to smoke a pipe while visiting the smallest room. We know that famous names such as Ludvig Holberg, Ole Rømer, H.C. Ørsted and Hans Christian Andersen studied in the Library, and probably also needed to visit the privy now and again – with or without a pipe.

Waste from the privy ran down into a large bricked-up container (the latrine pit), but despite experiments with open windows and double doors, the stench up in the Tower was almost overpowering. Water closets were installed in 1902 but the pit was not emptied until 1921, when nine truckloads of muck were shipped off.

The Bell Loft

Drying Loft and Peasant Museum

The bells of the Church of the Trinity hang in the Bell Loft, above the gallery and concert venue. However, the bells do not take up much space in the 900-m² loft, which has been rented out for all kinds of purposes over the years. At one stage, the people of Copenhagen discovered that it was an ideal spot in which to dry laundry. Later, it was used to store tanned hides, dried herbs, painted theatre sets and feathers for the fine clothes and hats of society ladies.

In 1880, Lieutenant Bernhard Olsen rented the loft and set up a peasant museum, which would become the Open Air Museum in 1901.

After the Great Fire of 1728, the Bell Loft was rebuilt from Pomeranian pine. The impressive original timbers are still intact and visible in the loft, which also houses the big clock from 1731, as well as many other objects that have stories to tell about the history of the Round Tower and the church.

The Round Tower Planetarium

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.

Uppermost on the facade of the tower there is a gilded inscription, a rebus. Christian IV's draft of it, written with his own hand, is kept at the Danish Record Office. The rebus can be interpreted in the following way: Lead God, the right teaching and justice into the heart of the crowned King Christian IV, 1642. 1642 was the year when the tower was completed.

Oldest observatory in Europe

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

The Round Tower has contained several different observatories. The latest is from 1929.

The observatory is 6.75 metres high and 6 metres in diameter and contains a refracting telescope with

80–450 x magnification.

Opening hours

Read more of the history of the Observatory

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.

The view