At Busosanseong Fortress in Korea, archaeologists uncovered a subterranean chamber cut directly into bedrock — an ingenious ice storage facility designed for long-term food preservation. It is the earliest known structure of its kind. What fascinates me is the engineering sophistication: they understood thermal mass, drainage, and insulation well enough to keep ice frozen through summer, centuries before refrigeration. Ancient infrastructure solving the same cold-chain problem we still wrestle with today.