The Fortress can be visited
Charles Fort

In Kinsale Bay in Ireland stands Charles Fort, a star-shaped fortress. Located directly on the water, it offered protection and control over the entrance to the bay.
History+
The origins of the site date back to an earlier fortification called Ringcurran Castle, which played a role in the Siege of Kinsale in 1601. In the 1670s and 1680s, under the direction of Sir William Robinson, the architect of the Royal Hospital Kilmainham in Dublin, the current star-shaped fortress was built. Its special design was intended to withstand cannon attacks. Charles Fort was of importance in the Williamite War from 1689 to 1691, especially during the Siege of Kinsale in 1690.
Source: Wikipedia · Licence: CC BY-SA 4.0
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.6965, -8.4990