The Fort can be visited
Fort de l'Éminence

Fort de l'Éminence is a French military structure located on Port-Cros island (Var). It is the largest fort on Port-Cros and was the basis of the island's defense in the 19th century. It was built in the 18th century, replacing a fort destroyed in 1793. It is located at an altitude of 140 m and is 25 minutes from the village.
History of the fort+
A first fort stood on this site, belonging to a defensive complex built on Richelieu's orders in 1635 to counter the Spanish threat, and which also included Fort de l'Estissac, Fort du Moulin, and Fort de Port-Man. It was destroyed by the English in 1793. The construction of the current fort began at the very end of the 18th century. It was interrupted by the fall of the Empire in 1814.
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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: 43.0085, 6.3885