Instead of climbing the stout Round Tower's stairs, visitors scale a smooth, 600-foot spiral ramp. Supposedly, Peter the Great of Russia once ascended this ramp on a horse alongside his wife, Catherine, who took a carriage. From its top, you enjoy a panoramic view of the twisted streets and crooked roofs of Copenhagen. The unusual building was constructed as an observatory in 1642 by Christian IV and is still maintained as Europe's oldest such structure.
The art gallery has changing exhibits, and occasional concerts are held within its massive stone walls. An observatory and telescope are open to the public evenings mid-October through mid-March, and an astronomer is on hand to answer questions.