The Round Tower is a 17th-century tower located in central Copenhagen, Denmark. One of the many architectural projects of Christian IV, it was built as an astronomical observatory. It is most noted for its equestrian staircase, a 7.5-turn helical corridor leading to the top, and for the expansive views it affords over Copenhagen.

The tower is part of the Trinitatis Complex which also provided the scholars of the time with a university chapel, the Trinitatis Church, and an academic library which was the first purpose-built facilities of the Copenhagen University Library which had been founded in 1482.

Today the Round Tower serves as an observation tower for expansive views of Copenhagen, a public astronomical observatory and a historical monument. In the same time the Library Hall, located above the church and only accessible along the tower's ramp, is an active cultural venue with both exhibitions and a busy concert schedule.

The Round Tower is a cylindrical tower built in masonry of alternating yellow and red bricks, the colours of the Oldenburgs. The bricks used were manufactured in the Netherlands and are of a hard-burned, slender type known as muffer or mopper. On the rear side, it is attached to the Trinitatis Church, but it has never served as a church tower.

Steenwinckel—whose name is otherwise synonymous with Dutch Renaissance architecture in Denmark—with the Trinitatis Complex has left his signature style. Unlike his other buildings with their lavish ornamentations and extravagant spires, the complex is built to a focused and restrained design. Hans van Steenwinckel must have been up on the situation in Holland, cogniziant that the style which he had once learned from Hendrick de Keyser had been altogether abandoned.