We stayed one night and saw quite a bit. Two nights is sufficient. This is a small city. We got there in the am and did a full day. The next day we went to the ship and walked to the Little Mermaid and the Resistance Museum (which was wonderful) from the ship (about a 5-10 minute walk on the pier area next to the ship.
We enjoyed the castles in town and did that day 1. We didn't visit Tivoli.
We ate at the SAS Radisson and the restaurant was very good. It also offers panoramic views of the city.
