The Mer de Glace (Sea of Ice) is a glacier near Chamonix that you can visit. In Summer, the frozen surface is undulating, and topped with lines of frost and snow, so it looks like waves, hence the name.
You access it via a rack railway that takes you to a station up in the mountains. When it was built, the glacier was about at that level, but nowadays, having taken the train up, you then have to take a new cable-car down, and then some 300 more steps down to reach the ice. The glacier is a lot smaller than it used to be.
Every tourist season, caves are carved out into the ice, and you can see there a small exhibition showing the discovery and early exploration of the glacier. If you're mad, you can ski down it too, access and departure being managed by helicopter.
The old train that took you up was this steam-powered one, burning 400 kilos of coal for each trip. The new one is comfortable, but less quaint.
These are the holes carved in the ice, and a small view of the exhibition.
A helicopter collects skiers from the glacier surface. And a view of the glacier from the other side of the valley. You can see the V-shaped glacier valley between the two mountains. 150 years ago the glacier came up to the level of the black line of rocks; these days you can barely see it. The railway line is the higher of the two tracks you can see on the mountain to the right.