Much more rewarding than Vallorbe itself is the rather wild and largely unvisited countryside around and about. Local trains and buses go everywhere but, with hourly schedules at best, they’re rather less convenient than your own transport.

Just over 2km southwest of Vallorbe are some caves, Les Grottes de Vallorbe (daily: June–Aug 9.30am–5.30pm; April & May 9.30am–4.30pm; Fr.12), forming a tunnel over the River Orbe and replete with impressive stalactites and stalagmites, along with an exhibition of minerals dubbed Le Trésor des Fées (Fairy Treasure). Some forty minutes’ walk from Le Day train station just outside Vallorbe is the Fort de Pré-Giroud (July & Aug daily noon–5.30pm; May, June, Sept & Oct Sat & Sun same times; Fr.9), an extensive military complex dug into a hillside in 1937 to defend against possible incursion by enemy forces over the nearby Col de Jougne from France. An innocuous chalet on the surface hides vertical shafts giving access to chilly labyrinthine tunnels and a whole subterranean bunker, complete with kitchen, dorms and a hospital, capable of supporting 130 people.

ROMAINMÔTIER, a small village in a secluded valley about 14km east of Vallorbe near Croy, has managed to preserve in near-mint condition its extraordinarily grand Romanesque priory church. Switzerland’s oldest monastery was founded on the same site in about 450, and the current building was constructed by Cluniac monks in 990–1028. The church – approached from the picturesque village street beneath an even more picturesque fourteenth-century clock-tower – reopened in late 1999 after several years of renovations. As you enter (daily 7am–6pm), you pass into the impressive and harmonious nave, with its massive piers and a vividly painted thirteenth-century vault overhead. On the left of the choir and chancel, with fourteenth-century frescoes, is the separate Chapel of the Holy Virgin, with a beautiful medieval statue of Mary. The remains of the cloister run along the outside of the south wall.

Continuing the ecclesiastical theme, MONTCHERAND, a tranquil village 8km northeast of Romainmotier with a view over the Orbe valley, shelters a small but notable tenth-century church (daily: May–Sept 8.30am–8.30pm; Oct–April 8.30am–6.30pm). Its most striking feature is a set of twelfth-century frescoes in the apse, depicting the saints Paulus, Ithos, Andreas, Jacobus, Matias and Filipus standing shoulder to shoulder in brilliantly restored colours.

ORBE, halfway between Vallorbe and Yverdon on the bus or train, is a picturesque old town up on a rock, with steep cobbled streets and another atmospheric church, a five-naved effort dating from the fifteenth century. Orbe was known to the Romans as Urba, and 2km north of the town, in a muddy field at the hamlet of BOSCÉAZ near the junction of the autoroute and highway, are some of the best Roman mosaics to be seen in Switzerland (Mon–Fri 9am–noon & 1.30–5pm, Sat & Sun 1.30–5.30pm; Fr.3; SMP). Nearest to the ticket hut is Pavillon IV, sheltering hexagonal mosaics of gods and goddesses, with the central medallions showing the deities of the seven days of the week. Further on, Pavillon III has a countryside procession, led by a trumpeter; and Pavillon II displays an intriguingly complex mosaic maze. Excavations of other areas are ongoing.