Visiting the soon-to-be-gone glacier
The Mer de Glace is slowly melting away. Make sure to visit it before it's finally gone. In the ice you can feel rocks from before the last ice age, and touch compacted snow which is almost as old as the Dinos.
Perfect way to spend a sunny summer day, while acknoledging climate change ( all the previous glacier levels are marked on the walls and documented with old pictures, essentially making the descent to it a veritable trip through time)