The Sigtuna monastery is simply beautiful. Hopping around there at eight in the evening, having the entire lake behind the castle and all green around it to yourself is just fantastic. Then it doesn't matter anymore that you cannot look inside the castle that once used to be a monastery.
Stockholm is a Potpourri of islands and the sort of place you have to hop. With lots of water in-between and around it, the difference to Hamburg is that the 'canals' are proper rivers, after all, Stockholm is nearer to the coast of the Baltic Sea. The island 'Södermalm' and a lock between Riddarholmen and Södermalm turned out to be very interesting places. Stockholm is a great place. And Sweden is beautiful.>