Architect couple Patrick Theis and Soraya Khan extended the basement of the five-storey House in Notting Hill Gate, stretching it beneath the front garden and part way under the rear garden.
The architects finished the new subterranean swimming pool, cinema room and gym with dark colours, aiming to bring in a sense of nature.
Grey tiling lines the pool, intended to be reminiscent of a mountain cave pool, while a long clerestory window brings in natural light from above. The vertical panels of aspen wood that cover storage areas are intended to represent a forest.
Conversely, the dark grey velvet finishes in the cinema were chosen as a reference to 1930s glamour.
Theis and Khan also added an extension to the rear of the property, using brick and glazing as a contemporary interpretation of the Victorian architecture of the adjacent houses.
Inside, the pair reconfigured the ground floor and the basement floor to include four split levels to improve lighting and views in the different spaces.
"We wanted to achieve a sense of fluidity and connection between all the lower reception floors to ensure there were no dead spaces within the house, rooms that are hardly ever used except for occasional events," the architects told Dezeen.
"We developed a split section which created interim levels between the conventional ground and basement."
A wooden staircase with a glass banister connects the four levels, with internal windows offerings views between the different spaces.
"With the open risers, visual connectivity and openness is achieved and each landing has a main window looking south towards the rear garden," explained the architects.
The open-plan kitchen and dining room are placed on the half level above the basement with sliding glass doors that open to the garden. A pantry, and the laundry room are also placed on this floor.
On the next level up, another dining room occupies the next level up occupying the rear extension. It is raised slightly above ground with windows beneath that provide light and views to the pool below.
The main entrance and living areas occupy the fourth level upper ground level.
To make better use of space in the bedrooms on the top three levels, the architects moved the existing staircase and replaced it with a twisted wooden version wrapped by a white banister.
The master bedroom and en-suite bathroom on the third floor open to a terrace, which features bushy planting that maintains privacy.
White paintwork, oak and porcelain tiling are used to finish the upper levels, while darker colours are used for the basement level.
Patrick Theis and Soraya Khan founded their Tunbridge Wells-based practice in 1995.
Their past projects include a colourful new headquarters for the RIBA, the refurbishment of an apartment in south-west London and their own home and studio in the east of the capital.
Photography is by Nick Kane.
Structural engineer: Cundalls
Mechanical and electrical: Will Potter Partnership
Quantity surveyor: Terry Comber Associates
Lighting: Nulty Lighting
Pool specialist: Advance Pools
Main contractor: Akarana
Interior decoration: Sarah Delaney Design
Landscape designer: Richard Sneesby