Location: Portsea. Price? $20 million and it's yours

Portsea cliff-top properties, squeezed onto an outcrop where Port Phillip Bay meets Bass Strait, are generally among the most expensive in Victoria and are tightly held by their wealthy owners.

Ms O'Halloran bought Ilyuka, which has beach access and a private jetty set on the tip of Mornington Peninsula, a favourite playground for Melbourne's rich and famous, in 1999 for $7.5 million.

Selling agent Ross Savas, from Kay & Burton, said Ilyuka, a Spanish mission-style, sprawling house built for American oil tycoon Harry Cornforth in 1929-30, would be marketed globally following a formal launch during the spring racing carnival.

The marketing campaign includes distributing to select buyers a five-minute, mini-movie that reportedly cost more than $200,000 to make with a film crew of 50, focusing on a day in the life of a fictional family called the Crawfords at Ilyuka.

A Channel Nine personality and face of spring racing, Brodie Harper, plays one of the family members, with her husband Heath Meldrum.

"It's an elite property that has always been owned by significant families," Mr Savas said. "Someone of great wealth will buy it and turn it into a family compound."

Sunning yourself on the beach or cliff-top among Victoria's corporate and social elite next to the likes of trucking magnate Lindsay Fox and investment banker John McIntosh comes at a cost.

The Sisters in nearby Sorrento sold in 2008 for $19 million and set a Victorian record, breaking the previous highest price set when art dealer Rod Menzies paid $18 million to Hamton developers for the Stonington mansion in Glenferrie Road, Malvern.

That sale broke the coastal record set in 2006 when the Mount Eliza estate of Sir Reginald Ansett was sold for $14.5 million. In 2003, Ms O'Halloran sold a 742-square-metre former "vegie patch", part of the estate, for $1.6 million.

RT Edgar real estate agent Warwick Anderson sold Ilyuka to the previous owner, property developer David Deague. "It's a very special property, no doubt about that. It's one of the best properties you can get on the cliff."

However, buyer advocate David Morrell said it would be difficult to get the $20 million asking price in the current market conditions.

"They're struggling to get $20 million for houses here in Melbourne; why are they going to pay that for a beach house?"

Matthew Baxter, director of valuers Market Line Opteon, said: "The market is softening but there's such a low supply of properties there that it will be a good test to see if the underlying demand is still there."

Portseas most exclusive addresses

The Sisters, 3080 Point Nepean Road, $19 million, 2008

Kiewa, 3818 Point Nepean Road, $8.75 million, 2010.

Inverary, 3624 Point Nepean Road, $8.71 million, 2010

Vacant land, 2 Point King Road, $7 million, 2006

House, 3096 Point Nepean Road, $9 million, 2010