Fort du Grand Langoustier, Military fort on Porquerolles Island, Hyères, France.

Fort du Grand Langoustier is a former military fortress located on the western edge of Porquerolles Island. The square stone structure features a two-level artillery tower with a terrace that overlooks the sea and surrounding waters.

The fortress was built between 1633 and 1640 under Cardinal Richelieu's direction to defend maritime traffic. It formed part of a broader strategy to secure French coastal defenses during this period.

The fort's name comes from the Langoustier point, where langoustes, or spiny lobsters, were once caught. Its square artillery tower, vaulted powder magazine and spiral stair show how French coastal defences worked. Today the site is opened to visitors only during the European Heritage Days.

The fort is normally not open for casual visits without permission. However, visitors can access it during special heritage events such as European Heritage Days in September.

The fort was spared when the English occupied Porquerolles in 1793, and in 1810 Napoleon had a passage cut through the northwest side to reach the ground-floor powder magazine directly. The battery was decommissioned in 1874 after the Repentance and Giens works entered service.