This is the view of the Mer de Glace from the top of the Montenvers railway, looking south-east. 200 years ago the top of the glacier was at the level from which the picture was taken.
The glacier is the biggest in France (7km long and 200m deep). In winter it is used as the run-out from the Vallée Blanche, one of the world's most famous ski-runs, which starts from the Aiguille du Midi.
From here we set off along a path to the right of the photo, then climbed down a couple of ladders to the level of the glacier.