Åselholm, on the Hällesö island is very picturesque small village with a visitor pontoon (in the centre of the picture on the right).
The island is accessible by car in 5h45 from Mariehamn, using three ferries, and in 3h45 from Turku, using one ferry. Otherwise, no public transport.
The shallow bay is well protected and the pontoon is very convenient. There is a small bay further south east where one can anchor.