The Val-de-Bénédiction Charterhouse is worth a detour. Once through the cloister gate, walk towards the main nave of the church which affords a superb view of Fort St-André. Visit the small cloister, the chapter house, the sextons' courtyard and the lavabo (circular building), then walk to the large cemetery cloister (20m wide and 80m long) skirting the monks' cells; one of these can be visited. Don't miss the frescoes decorating the chapel, the 18C fountain of St John's cloister and the hostel.