Not really a yachting destination, as there is no harbour, but accessible by day trip from Hanko in anything but the nastiest conditions, Bengtskär is the southernmost point of Finland. A tiny rocky island, its main attraction is Scandanavia's tallest lighthouse. The scene of an epic battle in the second world war, the lighthouse and its associated buildings (now a hotel) are now owned by a trust, and hosts thousands of day trippers every year.
Arrival is interesting, as the trip boat simply nudges up to rocks and stays there, rocking in the swell. You get a talk on the history of the place and then you are free to wander or climb the tower at will. There is a small cafe and a museum.
2006 is Bengtskär's 100th anniversary.
Note: Elina Mattila from Finland points out that it is possible (indeed popular) to get to Bengtskär with a yacht in settled weather, but you must take care. There is no shelter (apart from behind the island) but there are apparently rings in the rocks.