Fort du Trou-d'Enfer, Military fortress in Marly-le-Roi, France.
Fort du Trou-d'Enfer is a 19th-century fortress in Marly-le-Roi, sitting on wooded hills west of Paris. It consists of thick stone walls, casemates, and a central courtyard surrounded by defensive ditches.
The fort was built between 1878 and 1881 as part of a defensive ring designed to protect Paris after the Franco-Prussian War. After the First World War it lost its military role and was repurposed over the following decades.
The grounds were later converted into a pheasant breeding facility for presidential hunting, a use that continued until 2010. Visitors can still see traces of this unexpected purpose scattered across the property.
The fortress is not freely open to the public and visits are generally arranged through guided tours booked in advance. The ground is uneven throughout the site, so sturdy footwear makes the walk more comfortable.
After its military years, the site was used as a pheasant breeding facility for presidential hunting parties, a function it kept until 2010. Traces of that chapter are still visible across the grounds for those who look closely.
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