Ondol

An eleven-minute government-made record from 1941 shows how a traditional Korean ondol underfloor heating system is laid and fired, filmed on location during the colonial period and recovered decades later from a Russian archive. There's no plot, just a plain demonstration of a building technique, which is exactly what makes it useful to architecture and folklore researchers today.

Why it's free: Free on the Korean Film Archive's own channel; the archive holds the restoration rights to its collection.