#OTD in 1576.
The cornerstone for Tycho Brahe's Uranienborg observatory is laid on the island of Hven.
It was the first custom-built observatory in modern Europe, and the last to be built without a telescope as its primary instrument. Brahe abandoned Uranienborg and Stjerneborg in 1597 after he fell out of favour with the Danish king, Christian IV of Denmark; Brahe left the country, and the institution was destroyed in 1601 after his death.