This is the Chêne-Chapelle (Chapel Oak) of Allouville-Bellefosse in northern France. It is between 800 and 1,200 years old, and in the 17th century the local curé built a chapel inside it, believing that the lightning that struck the tree and hollowed it out was an event with a divine purpose. It has an altar for saying mass and a “hermit’s room” on the floor above! Photo by Thomas Pakenham, from Remarkable Trees of the World.