It’s the world’s biggest house for sale – and it's top secret

It says something about London’s affluenza that for the price of a five-bedroom penthouse in Connaught Place, Hyde Park, you could buy a whopping Italian estate with a 12th-century medieval castle and a sprinkling of Tuscan farmhouses in the grounds, where the number of bedrooms adds up to 115, with 100 bathrooms on the side. The first costs £20m and the second €28m (£19.8m).

This castle just east of Siena, wrapped in 630 hectares planted with 1,500 olive trees producing award-winning olive oil, is thought to be the largest property in the world currently on the market. But the Italian market is as keen on discretion as the Mafia is on anonymity, so even the name of this prize piece of history is being kept firmly under the estate agent’s pillow.

^{The lavish interior of the 11th-centry castle somewhere near Siena}

It will probably sell to one of those in the top 1 per cent of the richest people in the world – the ones who own roughly 99 per cent of the planet’s wealth – so the purchaser’s name, too, is likely to remain hush-hush. The setting in Tuscany, the medieval courtyard with tower and chapel, the Italianate gardens with palms and box hedges, the interiors with marble floors and elaborate painted ceilings, make it so romantic that it is sometimes hired for weddings. It goes without saying that there is plenty of room for guests to sleep, as well as pools for them to swim in.

“It is exceptionally beautiful. There are many castles in Tuscany but very few are medieval,” says the agent John Jonk of Sotheby’s International (0039 05507 51888; sothebysrealtycom). “The approach to it is wonderful and you go into another world. There are thousands of wild boar and roe deer, magical woods, vineyards, olive groves and grain fields. On the estate it is always silent. The castle was built at a time just before Giotto, when the Renaissance lay around the corner and Siena was at war with Florence.”

^{A view of the interior courtyard}

From the 1400s it had been in the hands of the Piccolomini family until the current owners bought it more than 30 years ago. “The price is unusually low considering it provides 154,139 sq ft of accommodation. But this reflects the market in Europe at the moment.” It is believed that Galileo Galilei stayed in the tower and must have gazed out upon the same night sky.

^{The property really is an authentic castle}

How does it compare to other global Godzillas of the property world? One of the largest newly built palaces is the 27-storey skyscraper Antilia in Mumbai, India, which provides 400,000 sq ft of space, including six storeys of parking lots, a lobby with nine elevators and several lounges, a ballroom with crystal chandeliers, swimming pool, bar, yoga studio, ice room, four-storey garden and private sleeping areas for a family of five. It is thought to have cost $2bn (£1.3bn) to build and is the home of Mukesh Ambani, head of the India-based petrochemical Reliance Industries.

^{The tasteful gardens}

According to therichest.com, the largest home is the Istana Nurul Iman Palace, at 2.15 million sq ft. This is the official residence of the Sultan of Brunei and has 1,788 rooms, 257 bathrooms, five swimming pools, a 110-car garage, air-conditioned stable for 200 polo ponies, banquet hall, and a mosque large enough for 1,500 worshippers. Its estimated cost was £1.4bn.

^{The brick interior}

In Britain, the largest property still used as a home is Windsor Castle at 484,376 sq ft, but that includes St George’s Chapel and Queen Mary’s Dolls House. Interestingly, the original castle was built in the 11th century, after the invasion of William the Conqueror, at just about the same time as the Italian castle was being built and the cathedral and Leaning Tower in Pisa were going up.

^{A view of the castle in its surroundings}