I have recently done some long walks on the Swedish west coast (västkusten aka. bästkusten). just to clear my head out. One of my all time favourites is Marstrand which is a small town situated on two islands named Marstrand and Koön. I was lucky with the weather and there weren´t many people there since the season begins around the beginning of June. Then the place is packed with tourists not only from foreign countries and neighbouring countries but from other Swedish cities as well. Marstrand is also an important sailing spot for people who are sailing on the Skagerrak. You can take bus 312 from Gothenburg Central to the island, it is around 50 minutes. Another option is (since they have one bus in every hour) to take either a bus or train to Ytterby Central and from there you can take another bus to the island. This would take you 1h 15 minutes. The ticket for an adult is approx. 80 SEK.
Click two times on the pics. It is all worth it. I promise.