Bohus Fortress, located in Kungälv, Sweden, was built in 1308 to defend Norwegian territory against Sweden. The fortress saw multiple attacks but was never captured. After being ceded to Sweden in 1658, it was used as a prison, with one notable prisoner spending 42 years behind bars. Despite plans to demolish it in the 18th century, much of the fortress still stands today and is open to visitors as a museum during the summer with guided tours. They also host a really cozy Christmas market where you can walk around the fortress while shopping for local handmade gifts and enjoying tasty holiday snacks and glögg.