The Seokguram Grotto, built in the 8th century, was analyzed for its intricate mechanism to survive against adverse ambient conditions for more than 1,200 years. Especially, the rotunda (round chamber) where the statue of Buddha sits is the major focus of this paper. Its original design (before any changes were made) was an ideal one which allowed vapor migration through the surrounding walls, preventing any aging problem due to vapor condensation within the chamber. Simple experiments were conducted to verify this by employing a simple model chamber with stone slabs of different porosity on top: granite (12cc/gram) and basalt (25cc/gram). As expected, the vapor adsorption capability of the slabs played a decisive role in condensation where coalesced water vapors were observed at the inner surface of the granite slab. No condensation took place for the case of basalt.