The elaborate building, known as “Putin’s Palace”, sits near the Black Sea resort town of Gelendzhik, in Krasnodar Krai. The palace featured in a viral video and an extended documentary released by Russian opposition leader, Alexei Navalny, in which he claims the magisterial structure belongs to President Putin.
The Kremlin denies this, with Putin himself denouncing the video as a “compilation and montage”, and “boring”.
He added: “Nothing that is listed there as my property belongs to me or my close relatives, and never did.”
Since the video’s release, vocal anti-Putin critic Mr Navalny has been jailed for three-and-a-half years by a court in Moscow for failing to stick to the terms of a suspended sentence.
He was detained after a stint in a Berlin hospital, recovering from poisoning with a nerve agent.
In the video, Mr Navalny claims the property cost £1 billion – financed by the “largest bribe in history”.
Close Putin associate, billionaire Arkady Rotenberg, has previously claimed ownership of the mansion, adding it was set to become a hotel in the future.
“Putin’s Palace” is thought to have undergone a near-total remodel since its initial construction.
Some reports describe its incredible opulence, with a cavernous master bedroom and corridors of guest suites – one claim even includes an indoor go-karting track.
READ MORE: Putin’s henchmen scramble to sell homes in annexed Crimea
The reason behind this would have been unwelcome to the Palace’s owner – a nasty mould infestation.
The mould was mentioned in Mr Navalny’s video, and was corroborated by two builders to the broadcaster’s Russian service.
The builder, whose real name was not published, said: “Walls and ceilings were covered in mould.
“Just ordinary mould – green. In places even black.
“It had affected the whole building. We were shocked.”
It is believed the complex required thorough disinfection at least twice.
Another builder added: “They kept building and demolishing, building and then demolishing.”
Here is the building’s location on Google Maps.