The title of the "largest fort in Europe" is most commonly held by the Fenestrelle Fortress (Forte di Fenestrelle) in the Piedmont region of Northern Italy. This massive alpine fortification, often called the "Great Wall of the Alps," covers an area of approximately 1.3 million square meters and stretches across three separate fortresses connected by a three-kilometer-long indoor stone staircase with nearly 4,000 steps. Another strong contender is the Fortified Castle of Sedan in France, which is recognized as the largest medieval fortress in Europe, covering 35,000 square meters. While Fenestrelle is larger in total acreage due to its expansive mountain layout, Sedan is more compact but holds the record for structural volume within a single castle complex. In 2026, both sites are major tourist destinations; Fenestrelle offers a grueling seven-hour "Royal Walk" tour for those wanting to traverse its entire length, while Sedan features an immersive 600-year history tour. Depending on whether you define "largest" by square footage of the grounds or the footprint of the central castle, these two sites represent the pinnacle of European military architecture.