This one-time Cistercian monastery, 28km southwest of Calatayud, dates from the 13th century but was closed down by government order in the 1830s. New private owners converted the extensive grounds into a formal wooded park full of caves and waterfalls. The visit to the monastery itself, conducted by megaphone-toting guides, is underwhelming, but the park is indeed beautiful, especially the Caprichosa waterfall and the Lago del Espejo (Mirror Lake). Avoid summer weekends, when the place gets overrun by crowds.
It takes about two hours to follow the signed route round the whole park. Part of the monastery now houses the rather overpriced 60-room Hotel Monasterio de Piedra (double from €125) and the complex has two restaurants.
On Tuesday, Thursday, Saturday and Sunday, Automóviles Zaragoza runs a 9am bus from Zaragoza to the monastery (€11, 2¼ hours), returning at 5pm.