Uranienborg (Danish: Uranienborg, Swedish: Uraniborg) was a Danish astronomical observatory operated by Tycho Brahe. It was built c. 1576 – c. 1580 on Hven, an island in the Øresund between Zealand and Scania, which at that time was part of Denmark. Shortly after its construction, the observatory was expanded with an underground facility, Stjerneborg, on an adjacent site.