Trekroner Søfort

Trekroner fort is located on an artificial island in the Copehnagen harbour, originally used to guard the harbour entrance.
I went with a chartered boat but I’m under the impression that you can buy a ticket on a boat from Nyhavn in the summer season or rent your own boat to get here (several of those pulled up to dock while I was on the island).
Fun little island with an abandoned fort. The surrounding grass covered berms are great to climb and offer views of the harbour. There are little water tower like structures but look to be old guard towers. These red and white checkered towers are very cute and very distinctive. The fort itself is open and you can explore the old storerooms, hallways, and miscellaneous rooms.
There is a café here, but I didn’t try it this time.
Really recommend it if you have a few hours extra and want to see a small part of Copenhagen that’s not typically on the well trod path.