Visingsborg, 16th century castle ruins on Visingsö Island, Sweden.

Visingsborg is a 16th century castle on Visingsö Island with visible foundations and tower remnants scattered across the site. The structure shows a square layout with a moat and traces of the southern wing walls.

The foundation was laid in the 1570s, using brick from the Alvastra monastery and a new brickworks in Gränna, after three villages were cleared from the site. Per Brahe the Elder built the west wing, his son Magnus the south and east wings, and Per Brahe the Younger added a north wing and a harbour in 1642. The castle was completed in the 1660s and abandoned in 1680 when the county was reclaimed by the crown.

Per Brahe the Younger kept a court at Visingsborg with a small army of about 200 men, a library and an armoury holding weapons for 800 men. A liveried trumpet corps played at table and accompanied him on journeys to Stockholm. On the island he founded a school in Kumlaby Church in 1636 despite church opposition, and its pupils sang psalms and polyphonic music at services in Brahe Church.

The ruin stands on the eastern shore of Visingsö, opposite Gränna, and is reached by ferry from the mainland. The surviving walls belong mostly to the southern wing, so look for them there. Boats on the island had to be gathered and locked during the prisoner years; today bicycles are the usual way to cover the island.

The 1718 fire was ruled an accident in the German guard detail's quarters in the castle's northeast corner, per lagman Brohman's January 1719 inquiry; the roughly 1,600 prisoners were then moved to Jönköping, Eksjö, Gränna and Växjö.