Stjärneborg, Underground astronomical observatory on Ven island, Sweden

Stjerneborg is Tycho Brahe's underground observatory on Ven island, built from 1581 to 1584 about 75 metres south of Uraniborg. Its instruments stood in separate stepped, crypt-like chambers sunk to solid rock, with only their roofs or domes rising above ground; these roofs could be opened or removed for observations. Excavated in the 1950s, the chambers now have a roof approximating the original and house a multimedia show.

Astronomer Tycho Brahe built the observatory in 1584 as a supplementary facility to his main observatory Uraniborg. Together, the two facilities made Ven island one of Europe's leading astronomical centers by the late 16th century.

The site reveals how scholars in the 16th century structured scientific work and valued stable observation conditions. The underground design reflects the thinking of that era, when scientists sought innovative solutions to improve their measurements.

The site is open from May through September and visitors experience the underground chambers through guided tours explaining the historical instruments. Sturdy footwear is recommended since the paths can be uneven and the air in the chambers remains cool.

The underground design was an ingenious solution to shield sensitive instruments from wind interference and enable far more precise measurements of celestial bodies. This innovative architecture shows how Brahe overcame practical challenges through creative building concepts.