The island is called Runö in Swedish.
Prior to 1944 the island was for centuries populated by ethnic Swedes and traditional Swedish law was used. Ruhnu has currently less than 100, mostly ethnic Estonian permanent inhabitants who like to keep to themselves.
A ferry runs from Munalaid in the mainland to Ruhnu. The trip takes approx. 4,5 hours. Bookings can be made via phone and internet .
The island is popular with hikers and swimmers, the best beach for swimming is Limo beach, with its "singing" sands.
The official Estonian tourism website provides an extensive list of options for accommodation in Ruhnu.