This Dutch Renaissance-style building is among many royal sights and buildings in Copenhagen, and was constructed by Christian IV in 1606 and was used as a royal summer residence until 1710. Rosenborg Castle is open for tours, and allows visitors to view a collection of royal items, including artwork and crown jewels worn by Danish royalty. After you visit the castle, take a stroll around the park that surrounds it, and admire the flowers that bloom in front of the castle in the summertime.