Uraniborg was an astronomical observatory and alchemy laboratory established and operated by the Danish astronomer Tycho Brahe. It was the first custom-built observatory in modern Europe, and the last to be built without a telescope as its primary instrument. Uraniborg was built c. 1576 – c. 1580 on Ven, an island in the Öresund between Zealand and Scania, Sweden, which was part of Denmark at the time.