Home to the Danish parliament, Folketinget. The island was originally 3 islands and was the original location ohe 2 previous castles burned down and can be visited in the basement - take a tour. Read more.
Amalienborg is a real royal castle although it doesn't have towers and spires. Read more.
This little green house across the street from Kastellet, is one of my favorite places to go in the morning for coffee. They have a great selection of teas as well. Read more.