Aggersborg is the giant of the Danish ring forts, and it is hard to appreciate until you see how much of it you cannot see. The circle, about 240 metres across, was twice the width of Fyrkat, with twelve gates, a rampart of earth and timber, and about forty-eight longhouses inside, set out in the same regular pattern of four-house groups. It was built around 980, in the reign of Harald Bluetooth, on a high bank above the Limfjord at one of its narrowest crossings, and it is thought to have controlled the water route through northern Jutland. A medieval church now stands on the site, and a section of the rampart is visible, along with markers showing where the gates and houses were.
The setting is wide and open. The Limfjord is a long, shallow, brackish waterway that cuts across northern Jutland and has made the area an island in all but name, and the fortress stood on its southern bank, facing the water. From the rampart you look north across the fjord to flat fields, with a ferry route nearby and the sky wide overhead. A small museum, the Aggersborg Viking Centre, helps explain the plan and the finds.
For a rider, northern Jutland is a place of space and wind. The roads are straight and flat, with long views across the fields to the fjord, and the weather changes quickly. A westerly can be strong, and showers cross the sky, with bright light between them. Traffic is light, and the main limit is the wind. The ferry across the fjord is a pleasant way to cross, and the small roads on either side are quiet. The best months are May to September.
The nearest small towns are Løgstør, with about 4,500 people on the fjord, and Fjerritslev and Brovst farther to the west, and for a larger place with a good supermarket you would use Aars, about 26 km away. Løgstør is known for its harbour and its old canning industry, and the fjord produces mussels and oysters. A plate of fish and chips or fried plaice at the harbour is a simple and good lunch. If you are following the Viking theme, this is the biggest fortress of the lot, and it is humbling to see how much work went into it.