Tycho Brahe’s observatory on the island of Hven was called Uraniborg. Built in the late 16th century, it was both a major astronomical research centre and an alchemical laboratory.
Construction began in 1576 after King Frederick II of Denmark granted Brahe control of Hven and supported his scientific work. Uraniborg was designed as a Renaissance palace of astronomy, with large precision instruments, living quarters, workshops, a printing press, gardens, and facilities for assistants. At the time, Hven belonged to Denmark; it is now known as Ven and lies in Sweden.
Brahe worked without a telescope, which would not become an important astronomical instrument until after his lifetime. His carefully calibrated quadrants, sextants, and armillary spheres produced exceptionally accurate observations of stars and planets. Those measurements later enabled Johannes Kepler to derive his laws of planetary motion.
A common mix-up is Stjerneborg, or Stjärneborg. That was a separate underground observatory Brahe built near Uraniborg to protect instruments from wind and structural movement. Uraniborg was the famous palace-observatory; Stjerneborg was its specialised companion facility.