The main sightseeing on Christiansø is provided by the walk along the fortified stone walls and cannon-lined batteries that mark the island’s perimeter.
There are skerries with nesting seabirds and a couple of secluded swimming coves on Christiansø’s eastern side. On the western side, a footbridge links Christiansø with the small neighbouring island of Frederiksø. Frederiksø's west coast has a swimming jetty and bird-watching spots.
The main formal sights are the two stone circular defence towers.