This Treehouse Chapel has been alive since Louis IX. In the late 1600s the tree survived a lightning fire that hollowed out the center. Interpreting this occurrence as a holy event, the local priest at the time called for the tree to be turned into a church. The tree was still growing under the kingdom of Louis IX and it survived the Hundred Years War with the English, The Black Death, the Reformation and the Revolution.
I thought this photo deserved to be big.
An artists version of it, that I found pretty cool.
Update: A few photos of what it looks like today: