One sunny afternoon, we took a ferry to Gressholmen, an island in the Oslo fjord. It has a large population of rabbits, and is often refered to as Bunny Island. The ferry service considered public transport and is covered by all the standard public transport passes.
Ferries leave for the islands frequently during the summer months form Vippetangen quay. We had to wait about twenty minutes for the ferry to Gressholmen, but we had a much shorter wait for the ride back. The journey there took about 10-15 minutes and is a good sight-seeing trip in itself.