The Citadel of Jaca is a fortification that they started building in 1592 when it was commissioned by Philip II when a French invasion was the big fear. Its real name until the 19th century was Castillo de San Pedro (or, St. Peter's Castle). Today it's all called the Jaca Citadel, and is surrounded with greenery. The Citadel is undoubtedly an impressive construction. It's one of the two in tact citadels in Europe. Its green lawn is often used by locals as a place to relax, walk their dogs or relax. I must admit, I do love the view at night from the Citadel, especially being at the bottom of the moonlit Oroel.