A 140 sqm (1,500 sq ft) basement set beneath a mansion house on Cadogan Square, Chelsea, forming the lowest level of a full seven-floor refurbishment on the Cadogan Estate, next to Knightsbridge.

The heart of the floor is a swimming pool lined in large grey stone tiles, with the still water and quiet lighting giving it the feel of a cave pool. A slot rooflight draws daylight down through the house and into a space that would otherwise sit in darkness. Alongside the pool are a gym lined in deep brown leather, a sauna and a steam room, together making a dedicated floor for relaxation.

The materials and detailing were chosen to feel calm and restrained, and to read as though the basement had always been part of the house rather than added beneath it. The result extends the home without disturbing its character.