The diving in Finland is predominantly wreck diving and due to the low salinity in the Baltic, the wrecks are in very good condition, even the wooden boats.
Kronprins Gustav Adolf, a Swedish man-o-war that sank in battle against Russia in 1788, was discovered by Finnish navy in 1995 and is now an underwater museum. Buy a ticket and get a plastic map to help you explore.
Hindenburg wreck was a 51 meter German icebreaker built in 1915. In 1918 she hit a mine and sank off Åland, before her discovery in 1995. She is well-preserved at 37-47 metres.
Nederland was a Dutch river barge, lost in 1917 on her way to the Russian grand duchy with a load of street bricks. The wreck is 35 metres long and 8 metres in width. She now rests on the sunken rock at Marhällan at a depth of 20-24 metres.