The Tramway du Mont Blanc, which links Saint Gervais to the "Nid d'Aigle" (Eagle's Nest), is under repair.
The work, which originally began in 2009, is being done to protect the railway lines. The work is very complex, not least because it is at 2400m altitude.
Just before the arrival at the Nid d'Aigle, between the two tunnels, workers are constructing a 60m long block of concrete above the track, to serve as a kind of paravalanche.
With two scheduled winter breaks, one this year and another next year, the project will continue until spring 2013.