Isabel II Fortress / Mola Fortress

Spain, Spain

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Isabel II Fortress, also known as La Mola Fortress, is a massive 19th-century military complex on the La Mola peninsula at the entrance to Mahón harbor in Menorca, Balearic Islands, Spain.

Construction began in 1847-1848 after demolishing the outdated San Felipe Castle, driven by fears of British return amid Anglo-French rivalries in the Mediterranean, and was completed in 1875 despite becoming obsolete due to advancing artillery technology.

Named for Queen Isabel II who visited in 1860, this monumental stone structure—Europe's largest 19th-century fortress—features ten defensive fronts, underground galleries, barracks, and coastal batteries, later serving as a prison before opening as a tourist site with panoramic harbor views.