the black beasts of the Massif Central

The 565 metre long, 120 metre high Garabit viaduct, built by Gustav Eiffel and opened in 1885. (survoldefrance.fr)

Les Betes Noires is actually a nicely composed and illustrated history of railways in the highly scenic Massif Central area in south-central France, more or less covering a rectangle of 100 km either side of a line running north-south from Clermont Ferrand to Béziers.  Although it isn't alpine, it is quite rugged and the altitudes achieved on the railway lines exceed 1,000 metres in several areas (the highest point is on the Translorézien line at 1,215 metres).  There are plenty of twisting trajectories though valleys and cols (passses) and impressive engineering works, the most famous being the Garabit viaduct. 

With low populations in most of the the towns and villages, some of the passenger services are under threat so it would be a good idea to travel over these lines while it is still possible.