I have a slightly inexplicable love affair with Denmark. It's not the most dramatically beautiful of landscapes, but from the moment I first landed there (in 2005) I just felt extremely comfortable.
As part of my 2005 trip, I spent a few days in Copenhagen, the most memorable aspect of which was a day trip to Roskilde to visit the cathedral and the viking ship museum. So when we found out that we'd have to pass through Copenhagen in order to get to Greenland, I suggested we extend our trip for just long enough to take in a couple of days in Roskilde.
The viking ship museum looks after the remains of three ancient ships which were found in the sea nearby. But the most interesting part, to me, is their reconstruction work. They've built replicas of all three of the Roskilde ships (and several other boats), frequently take them out to sea, and even sailed one of them across the Atlantic. There are enough videos and tales from the voyage to make a sea-loving girl's heart flutter.
Definitely a fun day out - if you love boats half as much as I do, then this is a worthy diversion from Copenhagen.
Also, it's hard to overstate the entertainment value provided by watching a group of uncertain tourists learning to row...
(At least none of them fell in the water!)