I took Alex to the Aven d'Orgnac. It is a cave formed by a river that must have ran through over 2 million years ago and shows the passage of the ice age. It's mostly a forest of stalagmites (which pile up from the ground); but it also has some natural red drapes hanging from the ceiling. The red colour is caused by the minerals in the water. The cave is still alive and growing, meaning that we can see the water dripping down and you can't actually see the stalagmite going up but you know it continues growing.
The best bit is that we found out we can do speleology which would enable us to explore further into the cave galleries. That's a great plan for next year.