Quite a bit of it. The steel-reinforced concrete structures are quite durable and it was more cost-effective to leave them in place than expend the resources to remove them. The postwar French Army refurbished some of the line in the 1950s and 60s and there was some early thought that they would be useful as shelters against a Soviet nuclear attack and as rear command posts for a Central European war. But this use was only for a few of the larger Maginot fortresses (ouvrages), and most of them were abandoned. The 1970s saw some effort at historic preservation and refurbishment and there are a number of them that act as museums. The largest fortress at Hackenburg is a museum as is the fortress at Schoenenbourg. The Alsace tourism department has a run down of some of the region's fortresses open to the public here as well as bicycle trails. The French Alps also has a number of sites open to the public, as this tourist report from 2002 describes. The Fermont Musuem is one of the more common Maginot tourist destinations and this video conveys some aspects of the guided tour such as subterranean trolley ride.