Alvsborg Fortress in Göteborgs Stad

You're standing on Kyrkogårdsholmen, a small island near the mouth of the Göta River, at the fortress of New Älvsborg. Take a look at the water around you. When this fort was built, this river mouth was Sweden's only way out to the North Sea and the Atlantic. Norway lay to the north, Denmark to the south. Whoever guarded this spot guarded a whole country's door to the sea.