The Fort can be visited
Fort Regent

On Mont de la Ville in Saint Helier, Jersey, stands Fort Regent, a 19th-century fortification. This fortress today also houses a leisure center and is a landmark on the island.
History+
The history of Mont de la Ville, where Fort Regent stands, dates back a long time. Even before the construction of the fortress, a dolmen was discovered here in 1785, which was later moved to England. In the Middle Ages, the hill served as common land, and in the 16th century, there were plans to relocate and fortify the town there, but these were never realized. The first signs of fortification, in the form of earthworks, are documented from 1757. The construction of Fort Regent began during the Napoleonic Wars on November 7, 1806. Under the direction of George Don, then Lieutenant Governor of Jersey, the fortress was completed in eight years with an average of 800 workers and named in 1814 in honor of the Prince Regent.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://en.wikipedia.org/wiki/File:Fort_Regent_rampart_1.jpg
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: 49.1812, -2.1061