A penthouse flat in London’s Knightsbridge neighborhood hit the market last week, asking just under £20 million (US$25.45 million).

The current owners purchased segments of the property 10 years ago and are selling because they decided to move into a house, according to Harry Dawes of Knight Frank, the listing agent for the property.

“What they’ve created is really leagues above what you see in private central London,” Mr. Dawes said.

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“The key part of this apartment is that it’s a lateral penthouse,” Mr. Dawes continued, explaining that the vaulted ceilings and plethora of outdoor space is possible only because the penthouse encompasses three different buildings. The top floor of three separate townhouses were reconstructed and re-landscaped to create a conjoined, lateral space.

Noting the difficulty of such an amalgamation process, Dawes said, “This was 15 years in the making. It’s a very special flat.”

“There’s an incredible amount of outside space,” he continued.

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Above the courtyard, Dawes said, is a rooftop terrace with “classic Knightsbridge skyline views.”

The five-bedroom property, located just south of Hyde Park, offers 4,699-square-feet of livable space, according to the listing. Calacatta, Ruivina, and Moon Rock marble flooring greet guests upon entry, leading outward toward a south-facing terrace overlooking Cadogan Square. Two additional terraces finish the home’s outdoor space.

The Pont Street property is listed Grade 2 in England, recognizing its special architectural and historic interest.

Knightsbridge, an affluent neighborhood with various ornate Victorian homes, offers its residents many garden squares, high-end restaurants and shops, and the Victoria and Albert Museum.