The archipelago around Gothenburg (southern and northern) is absolutely something you should visit. Its easily reached from Gothenburg, especially during this summer, when you can take a boat directly from the city centre out to the islands.

Suggestions southern part: Styrsö, Vrångö
Suggestions northern part: Hönö, Rörö

http://www.goteborg.com/en/archipelago/
http://www.goteborg.com/en/good-to-know/getting-to-the-archipelago/

From our house, take tram nr 1 from Munkebäckstorget towards Tynnered. Get off at Stenpiren and take the ferry from there.
The southern archipelago is within Gothenburg city, which means you travel on 2 coupons, the northern archipelago is Öckerö kommun, so 3 coupons.