The Round Tower (Rundetaarn), Copenhagen

A royal tower for science and the stars

Built between 1637 and 1642 under King Christian IV, the Round Tower was conceived as a monumental home for astronomy at a time when Denmark wanted to stand at the forefront of scientific discovery. Rising from the Trinitatis Complex, which also includes Trinitatis Church and the former university library, it offered scholars an elevated, stable platform above the city smoke to chart the heavens and refine navigation in an age of exploration. From the outside, the tower’s cylindrical brick form stands out against the surrounding roofs of Indre By. A band of gilded letters, personally sketched by Christian IV, winds around the façade as a cryptic rebus invoking learning, justice and divine guidance for the king. This fusion of piety, power and scientific ambition set the tone for a building that has always been more than just a viewpoint: it was designed as Copenhagen’s “star castle,” a statement of royal investment in knowledge.

The remarkable spiral ramp within

Step inside and instead of a staircase you find a broad, whitewashed spiral ramp that coils 7½ times around a hollow core to reach the top platform, almost 35 metres above street level. The ramp was engineered so that horses and carts could haul heavy astronomical instruments up to the observatory, avoiding steep, narrow steps. Its cobbled surface and gentle gradient make the ascent feel more like walking a sloping lane than climbing a tower. Over the centuries, the ramp has seen some unusual ascents. In 1716, Tsar Peter the Great reportedly rode up on horseback, and in 1902 a motor car was driven all the way to the top, proving the ingenuity of its design. Today, the slow spiral reveals changing perspectives on the tower’s brickwork, niches and thick walls, with small windows offering glimpses of the city outside as you gradually rise above the rooftops.

Library Hall: from bookshelves to cultural stage

Roughly halfway up, the ramp opens into the spacious Library Hall, originally created to house the University of Copenhagen’s book collection above the church below. For generations, this was a centre of scholarship, where theologians, astronomers and students worked under the timbered ceiling surrounded by shelves of volumes. The hall has deep literary connections: a young Hans Christian Andersen came here soon after arriving in Copenhagen, and he later wove the tower into his imaginative universe, even likening a giant dog’s eyes to its size in a fairy tale. Today, the room functions as a flexible cultural venue, hosting changing art exhibitions, design shows, concerts, talks and seasonal events that keep the building vibrantly in use rather than preserved as a static monument.

The observatory and Copenhagen panorama

At the top, the ramp gives way to a final short staircase and an open platform encircling the observatory. The Round Tower is widely recognized as Europe’s oldest functioning observatory building, and although the instruments have been renewed over time, it still serves as a place to peer at the moon, planets and star clusters through a refracting telescope on selected evenings. The viewing platform offers a 360‑degree panorama over Copenhagen’s copper spires, red rooftops and narrow streets. From here you can pick out landmarks from the old harbour to church towers and newer high‑rises at the city’s edge, tracing how the capital has grown far beyond the compact Renaissance centre that the tower originally surveyed. In clear weather the light over the Øresund and the orderly geometry of the city’s blocks give a calm, almost model‑like quality to the scene.

A living landmark in the heart of the city

Although its scientific role has shifted as modern observatories moved to darker skies, the Round Tower remains an active part of Copenhagen’s cultural life. The building frequently hosts thematic exhibitions, seasonal installations and occasional astronomy events that reconnect visitors with its original purpose. Its central location on busy Købmagergade means that stepping inside is like ducking out of a shopping street into a time capsule of 17th‑century brickwork and royal ambition. The tower’s relatively gentle ascent and covered interior make it accessible in varied weather, while the mix of history, architecture, views and arts programming appeals across ages and interests. More than three centuries after Christian IV’s masons laid the first stones, the Round Tower continues to do what it was built for: lifting eyes – and thoughts – above the everyday city to a wider horizon.