Survivor of no fewer than 14 sieges, the hulking ruins of Bohus Fästning stand on an island in the Nordre älv, near Kungälv. Founded in 1308 by the Norwegian king to protect Norway’s southern border, the fortress was inherited by Sweden at the Peace of Roskilde in 1658.
Take the Västtrafik Grön Express bus from Göteborg to Kungälv (30 minutes, every 10 to 15 minutes); get off at the Eriksdal stop and walk the remaining 500m.
Inside the castle, you can peer into the lightless dungeons of the rough-hewn round stone tower, Fars Hatt, where unfortunates were once imprisoned for witchcraft and heresy, and climb the battlements for a lofty view.
