A soot-streaked stone slab, a crooked channel under a floor, and an archaeologist who smells smoke from an age you thought was all stone and cold. You can almost hear a family slipping their feet onto a warm floor while winter storms howl outside.
Archaeologists digging late Bronze and early Iron Age settlements in the Korean peninsula keep finding the same odd setup: a hearth tucked into a kitchen wall, a flue that runs under a packed-stone floor, and a layer of ash that never spread into the living space. Those features show up across Mumun pottery sites (c. 1500 to 300 BC) and into early Gojoseon era layers, so the idea was around at least 2,400 to 2,500 years ago. Kim Won-yong (김원용), the mid-20th century archaeologist, argued these were deliberate underfloor heating systems, and later digs have only added more examples.
So when you step onto a warm floor in a Seoul apartment, you're standing on an idea that was invented thousands of years ago and kept evolving. Modern thermostats are new, but the basic brainwave is ancient and stubbornly good.