…be glad you don’t have to go to this one!
According to this blog, it’s “perhaps one of the most remarkable sights in France, a chapel perched on a volcanic plug. This is the Rock of Aiguilhe, on the edge of the town of Puy en Velay, in the Auvergne. The Chapelle Saint-Michel has stood there for 1042 years, since Bishop Gothescalk had it built in 962 on his return from a pilgrimage to Santiago del Compostella in Galicia. In 1955 workers found relics under the alter that had been there since it was built.”
Needless to say, parking is difficult. Seriously, check out 20 Unusual Churches (Part II) | Village Of Joy which has more fascinating church structures (and I say structures because some of them are barely buildings).