On the top of the Vomero hill there is a tufa fortress with a star shape: Castel Sant’Elmo. A medieval castle, it has been a fortress and a prison, and now contains auditoriums and exhibition centre. It offers a beautiful view over Naples and the surrounding area. The nearby Certosa di San Martino is a fine example of baroque architecture. Besides the church, cloisters and gardens, it hosts the Museum of San Martino.