This 12-sided church is one of the best preserved of its kind in Europe. Built in the early 13th century by the Knights Templar and based on Jerusalem's Church of the Holy Sepulchre, it once housed a piece of the Vera Cruz (True Cross), which now rests in the nearby village church of Zamarramala (on view only at Easter). The curious two-storey chamber in the circular nave (the inner temple) is where the knights' secret rites took place.