…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).