A very popular excursion when visiting Gothenburg is to take a boat trip out to the Älvsborgs fästning fortress, built in the 17th century as protection against the Danes, with a beautiful church towering from atop the island.
The fortress has been carefully restored and the entire island is beautifully maintained, with lush and inviting green lawns perfect for summer picnics. There are also several daily dramatized tours through the fortress and around the island, with actors playing the roles of 17th century priests and prison guards down in the dark dungeons. The 30-minute boat ride through the magnificent archipelago seascape is in itself an experience well worth the trip.
The 18th century Gunnebo castle outside of the city is another good choice for a day trip. This is a beautiful neoclassical castle with a wonderful park for leisurely strolls, a café, a restaurant and an interesting shop, open year round. Gunnebo can be reached by bus from downtown.