Copenhagen

Copenhagen Airport is so close to town that the city feels like an extension of the terminal. Both the metro and the train leave from Terminal 3 and reach central Copenhagen in around 15 minutes. Ride the metro to Kongens Nytorv and you are a few steps from Nyhavn's painted harbor houses, with the royal palace at Amalienborg and the Little Mermaid a walk along the waterfront. Rent a city bike if the weather allows: the center is flat and built for it. A five-hour gap is enough here, which makes Copenhagen the safest bet on the list for a nervous first-timer.