A short wooden footbridge connects Christianso to its smaller neighbour Frederikso, named after Frederik IV. The whole island can be walked across in five minutes. At its centre is the Lille Tarn, the smaller of the two original gun towers — beheaded by a Swedish naval bombardment in 1808 and rebuilt at a lower height, it now houses a small exhibition on the maritime history of the archipelago.
Frederikso has the harbour, a couple of artists' workshops, and the islands' boatbuilders. Sit on the rocks at the western end and watch the eider ducks pile up in the lee of the breakwater. Combined with Christianso, the two islands give you about two kilometres of coastline to wander.