It was Midsummer last weekend. It's not celebrated in England but it's quite a major event in Finland and some other countries including Sweden. I've never been too fond of it so I haven't bothered celebrating it here in England, I just read about it in blog entries and postcards, and look at the pictures. :D
Åland islands are technically a part of Finland, but have a lot more in common with Sweden than Finland. Midsummer seems to be no exception here - most Finns light a bonfire while Swedes (and Swedish speaking Finns?) have maypoles ((majstång or midsommarstång). It's an activity that attracts families and many others. People dance around the pole, listen to traditional music and some even wear traditional folk costumes. In addition, many wear crowns made of wild springs and wildflowers on their heads.
The stamp was issued earlier this year and shows a painting by Victor Westerholm, the founder of an artist colony in Önningeby, Åland and who therefore became quite a significant artist in Åland.