Built as an astronomical observatory, it is noted for its equestrian staircase, a 7.5-turn helical corridor leading to the platform at the top (34.8 meters above ground), and its views over Copenhagen.

[citation needed] Longomontanus' initial proposal was to erect the new observatory on the top of the hill Solbjerget, now known as Valby Bakke.

But since there were also plans for the construction of a new students' church and a library for the university, the idea of merging the three buildings into one grand complex emerged.

Although there is no clear proof, it is generally accepted that Hans van Steenwinckel the Younger was charged with the commission to design the new edifice though he did not live to see the tower completed.

When Hans van Steenwinckel died on 6 August 1639, Leonhard Blasius was brought to Denmark from the Netherlands as new Royal Building Master.

Unlike his predecessor, he would become a mere transitional figure in Danish architecture, dying just four years after his arrival in the country without leaving any notable buildings of his own design.

Instruments were growing still larger while the tower could not be expanded and, at the same time, light pollution from the surrounding city and vibrations caused by the ever increasing traffic in the streets below had made the observations inaccurate.

Hans van Steenwinckel must have been up on the situation in Holland, cognizant that the style which he had once learned from Hendrick de Keyser had been altogether abandoned.

[3] The architects now setting the agenda in the Netherlands, masters such as Jacob van Kampen (Amsterdam City Hall), Pieter Post (Mauritshuis in the Hague) and Philip Vingboons, now favoured a style characterized by sobriety and restraint.

[3] Instead of stairs, a 7.5-turn spiral ramp forms the only access way to the towertop observatory as well as the Library Hall and the Bell-Ringer's Loft, both located above the church.

The ramp turns 7.5 times around the hollow masonry core of the tower before reaching the observation deck and observatory at the top, on the way also affording access to the Library Hall as well as the Ringer's Loft.

Built in 1929, the current observatory is 7 m high and has a diameter of 6 m. Access is by a narrow winding stone staircase from the observation deck.

The rebus can be interpreted in the following way: Lead Jehovah, the right teaching and justice into the heart of the crowned King Christian IV, 1642.

[8] The tower contains a toilet which consists of a seat almost at the top and a shaft leading down to the bottom floor built into the hollow core.