Grotte des Demoiselles is an amazing network of underground caves near Provence and the Cevennes National Park. Reached by a small funicular railway, the caves can only be explored in small groups with a guide. The spectacular stalactites and stalagmites, some of which are four or five stories high, are simply out of this world. The largest cave made me go weak at the knees with vertigo so be prepared! The caves were fitted with pathways, staircases and stone balustrades in the 1930s which add to the experience - I was constantly reminded of the optical illusions of Escher (the never ending staircase!).
If you can ignore the obligatory tackiness of the visitors centre/cafe, tune out the prattle of the guide and simply admire the natural beauty of this place then you'll be sure to enjoy these grottos.
Price wise it was a little steep (c. £10 each) but the group sizes were small and it didn't seem too busy (we went in late June).
I can't help thinking if this was somewhere a little more accessible it would be deemed a natural wonder.
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