Rundetaarn

Instead of stairs, the Round Tower (Rundetaarn) is climbed by a wide spiral ramp that winds about seven and a half times around its hollow core to the top. Christian IV built it in the 1630s and 1640s as an astronomical observatory, and it remains one of the oldest working observatories in Europe. The ramp was reportedly built so that a horse and carriage could reach the summit, and Peter the Great is said to have ridden up it on horseback in 1716.

Partway up, a door opens onto the Library Hall, which once held the university's books and now hosts exhibitions and concerts. Near the top, a glass floor looks straight down the tower's core. The open platform at the summit gives wide views over the rooftops and spires of Copenhagen's old town.

Drawing more than half a million visitors a year, the tower suits families and anyone after a view without a steep climb. Most visits take under an hour.