Deep in the Badlands, Twilight, Rainbow Dash, and Fluttershy lead an expedition to the ancient, lost city of Petrot, which had survived for decades during the first reign of Discord two and a half thousand years ago. There, they uncover fabulous treasures and ancient knowledge, as well as unsettling hints about the possible history of Equestria and its immortal sovereigns.
*Fair Warning*
The canon for this story ends just before the Canterlot Wedding two-parter.