I turned 44 in June. I have this tradition – when possible – of not being in Belgium for my birthday. From Sweden in 2013 to the Châteaux of the Loire Valley in 2014, Lake Orta in 2015, Rome in 2016, London in 2018, North Carolina and Virginia in 2019, England in 2022, and Rotterdam in 2023. In June 2025, I headed to Copenhagen in Denmark with Steve.
After Amalienborg, we went to the Rundetårn or Round Tower in the centre of the city.
The Round Tower is a 17th-century structure constructed under the reign of King Christian IV as part of a wider programme of architectural and scientific modernisation.
Completed in 1642, the tower originally served as an astronomical observatory and remains notable for its unique equestrian spiral ramp, which ascends 7.5 turns to a viewing platform 34.8 metres above the ground, offering panoramic views over the city.
The tower forms part of the Trinitatis Complex, which also includes the Trinitatis Church and an academic library—facilities that became the first premises of the Copenhagen University Library, originally founded in 1482.
Historical background
In early 17th-century Europe, astronomy had gained significant importance due to increasing demands for maritime navigation during the age of colonial expansion.
National observatories were being established across the continent, with the first at Leiden in the Netherlands in 1632. The Round Tower, referred to in Latin as Stellæburgi Regii Hauniensis, followed in 1637, placing Denmark at the forefront of astronomical research.
After the exile of Tycho Brahe, Christian Longomontanus—his former assistant—became royal astronomer and professor at the University of Copenhagen. In 1625, Longomontanus proposed the construction of a new observatory to replace Brahe’s demolished Stjerneborg.
While he initially suggested building it on Solbjerget (modern-day Valby Bakke), the project evolved into a broader initiative combining an observatory, a university library, and a church within a single architectural complex.
The location was chosen for its proximity to the university and the Regensen dormitories, on land acquired by Christian IV as early as 1622.
The commission for the project likely went to Hans van Steenwinckel the Younger, though definitive evidence is lacking. Steenwinckel did not live to see the tower completed, dying in 1639. Construction began in November 1636, with materials sourced from the city’s ramparts and from Roskilde. High-quality bricks were imported from the Netherlands, as local production could not meet the desired standards. A contract was signed in 1637 with Henrik van Dingklage of Emden to supply the necessary materials.
Construction began in earnest after the demolition of pre-existing buildings on 18 April 1637 by a workforce of 200 men. The foundation stone was laid on 7 July 1637. Following Steenwinckel’s death, Leonhard Blasius, brought in from the Netherlands, took over but died in 1643 without making a significant architectural mark. The tower was completed in 1642, while the church and library were finished in 1657. During construction, churches across Denmark and Norway were compelled to contribute financially due to periodic funding shortages.
Scientific use and decline
Christian Longomontanus served as the first director of the observatory. In the aftermath of the Copenhagen Fire of 1728, the Trinitatis Complex was damaged but subsequently restored. It is believed that some astronomers lived in the tower to remain close to their work. Among the first was Peder Horrebow, who lodged there in 1753.
By the 19th century, the tower had become obsolete for scientific observation. The growth of the city introduced light pollution and vibrations, while the confined space could not accommodate newer, larger instruments. In 1861, the University of Copenhagen inaugurated the Østervold Observatory on former city fortifications, designed by Christian Hansen.
Notable ascents
The Round Tower’s spiral ramp has played host to several unique ascents. In 1716, Tsar Peter the Great famously rode up the ramp on horseback, with his wife Catherine I following in a carriage. A Beaufort car became the first motorised vehicle to ascend the tower in 1902.
Bicycle races have taken place since 1888, including a 1911 event organised by the newspaper Socialdemokraten. In 1971, Ole Ritter won a race to the top in 55.3 seconds; Henrik Djernis set a faster time of 50.05 seconds in 1993. Thomas Olsen holds the unicycle record, having completed the ascent and descent in 1 minute and 48.7 seconds in 1989.
Architectural design
Constructed of alternating yellow and red bricks sourced from the Netherlands, the Round Tower reflects the colours of the Oldenburg royal house. Although physically connected to the Trinitatis Church, it has never served a liturgical function.
The overall design is attributed to Hans van Steenwinckel the Younger, known for his Dutch Renaissance style, but the Trinitatis Complex marks a shift towards Dutch Baroque or Dutch Classicism.
This later style, influenced by architects like Jacob van Campen and Pieter Post, emphasised sobriety and symmetry, drawing on the writings of Andrea Palladio and Jacopo Barozzi da Vignola.
Spiral ramp and observatory
The internal spiral ramp is the tower’s defining feature, replacing stairs with a helical corridor built around a hollow core. Designed to allow horse-drawn carriages to reach the upper levels, it was essential for transporting books to the library and instruments to the observatory.
The ramp measures 210 metres in length, ascending 3.74 metres per turn. The outer wall has a length of 257.5 metres with a 10% incline, while the inner corridor is steeper, with a 33% incline over 85.5 metres.
The observatory platform is crowned with a small domed building, completed in 1929, which stands 7 metres high with a 6-metre diameter. It is accessed via a narrow spiral staircase from the platform below.
The observation deck itself features a wrought-iron lattice installed in 1643 by court metalworker Kaspar Fincke, incorporating Christian IV’s monogram and the inscription ‘RFP’, an abbreviation of his motto Regna Firmat Pietas (“Piety strengthens the Realms”).
Façade and features
The upper section of the tower bears a rebus inscription drafted by Christian IV himself, which includes the four Hebrew consonants of the Tetragrammaton. The message may be interpreted as: “Lead Jehovah, the right teaching and justice into the heart of the crowned King Christian IV, 1642.” Inside the tower, a shaft-built latrine descends from near the top of the structure to the base.
Contemporary use
Today, the Round Tower functions as an observatory for the public and amateur astronomers, primarily open from mid-October to mid-March. It also serves as a cultural venue and museum.
Since 1987, the former university library above the church has been repurposed as the Library Hall, now hosting art, science, and historical exhibitions, along with approximately one hundred concerts each year.
Views from the Tower
The viewing platform offers wide-ranging vistas across the rooftops of historic Copenhagen. Prominent landmarks visible from the tower include the Marble Church, Christiansborg Palace and Slotskirke, the Nikolaj Contemporary Art Centre, Copenhagen City Hall, the Church of Our Lady, Rosenborg Castle, and the Church of Our Saviour. On clear days, the Øresund Bridge and even parts of Sweden can be seen.
Unicycle race
A unicycle race is held each spring, with participants required to ascend and descend the spiral ramp. The current world record, set in 1989 by Thomas Olsen, stands at 1 minute and 48.7 seconds.
Cultural significance
The Round Tower features prominently in Danish cultural life. In Hans Christian Andersen’s tale ‘The Tinderbox‘, the largest dog is described as having eyes “as big as the Round Tower in Copenhagen”.
In ‘The Elder-Tree Mother‘, Andersen writes of a couple reminiscing about climbing the tower.
In his novel ‘To Be, or Not To Be‘, the protagonist Niels Bryde is born and raised in the Round Tower, where his father is a gatekeeper. A one-third scale replica of the tower stands in Solvang, California, a city founded by Danish immigrants.
The tower also lends its name to asteroid 5505 Rundetaarn and is frequently referenced in Danish idioms and comparisons. The Round Tower appears in the 2013 edition of the video game ‘SimCity‘.
A visit
Your visit to the Rundetårn will likely be quite short. There is a ticket booth at the base of the tower. The equestrian staircase is not too steep. There are several intermediate stops you cab make, including a look at the loo.
For the final part, wait for a green light. And when it’s green, be quick. A nice view of the city awaits you upstairs. Weirdly, I didn’t take photos of the staircase.
We were there on the 21st of June, my birthday but also the Greenland National Day.
Greenland National Day, known in Greenlandic as Ullortuneq and in Danish as Grønlands nationaldag, serves as a celebration of Greenlandic national identity. The day was established by the former Home Rule government in 1985. It later gained added significance in 2009, when Greenland assumed self-government on the same date.
National Day is marked across all Greenlandic communities. Typical celebrations include morning songs, coffee gatherings, flag-raising ceremonies, official speeches, and a range of cultural activities such as traditional folk dancing, musical performances, and kayaking displays.
Since 2016, Greenland National Day has also been recognised as a flag day in Denmark. On this date, Danish state authorities raise the flag of Greenland as a formal gesture of acknowledgment.
That was very visible in Copenhagen.
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