We wandered towards Kastellet, which is one of the best preserved star fortresses left in Northern Europe. It's an earthwork fort, so the walls are essentially big hills. Anyway, it's basically a big park, but is still used by the Danish military.

Unfortunately, there wasn't much in the way of signage, so we didn't really learn about the fort. This may be because it's still actively used by the military. We just wandered around the top of the fort, which offered a nice view of the surrounding area. We did see a windmill and a few cool buildings, but between the heat and the lack of signs, we weren't terribly impressed.