London's wealthiest homeowners are digging down instead of building up, carving multi-level basements so large that some hold more square footage below ground than the house above it, earning them the nickname 'iceberg homes'. This BBC film counts roughly 2,000 such basements dug in central London over the past decade, and goes behind the hoardings to see what's inside: cinemas, swimming pools, squash courts, wine cellars, beauty parlours, and servants' quarters, some taking up to three years to complete. It talks to the builders and owners paying for the excavations, and to the neighbours living through years of concrete mixers, lorries hauling away soil, and constant noise. The Royal Borough of Kensington and Chelsea appears as the council trying to regulate how many basements can be dug and how much disruption residents have to tolerate. The film stays close to the conflict rather than the architecture alone, framing mega-basements as a fight between what money can buy underground and what it costs the people living next door.