At the historic 19th-century observatory, scientists deciphered the composition of the sun and made the first weather forecasts. Today, Sonnenborgh is a museum where visitors can conduct their own research. Climb the stairs to the observatory and wonder at the starry heavens on an Star Viewing Night. Learn all about the unique building, the stars overhead and the weather in one of our exhibitions, tours or lectures. Sonnenborgh was built on a monumental 16th-century bastion, and is one of the best-preserved city wall bastions in Northern Europe.