8th-century Great Mosque of Córdoba converted to a cathedral after the Reconquista, hypostyle of 856 columns. Inscribed 1984 as part of the Historic Centre.
From Wikipedia
The Mosque–Cathedral of Córdoba is the cathedral of the Roman Catholic Diocese of Córdoba in the Spanish region of Andalusia. Officially called the Cathedral of Our Lady of the Assumption, it is dedicated to the Assumption of Mary. Due to its status as a former mosque, it is also known as the Mezquita and, in a historical sense, as the Great Mosque of Córdoba.