Many have commented on the topic, but the reality is no one knows. That's because few of the most valuable trophy properties go on the market any given year, and even less actually sell. While we have a partial list of properties that have sold in recent years (according to public reports), and we have some estimates of building costs, and some tax assessment data, many of the trophy properties we can really only speculate about what how much they would sell for at any given time.

Can you compare a condominium in New York City to a massive palace in a world capital, or huge beachfront property in Malibu or Palm Beach? Can you compare massive single family homes to an island, or a ranch bigger than some countries? For fun, we can try, but it's just speculation. So here is my list of properties that can make a case for being among the most valuable trophy properties. All of these properties have a limited number of potential buyers, but let's start with the ones that have very limited prospects for changing hands (for various reasons).

• Buckingham Palace is arguably worth 10 figures, but it's unlikely to ever be on the market in our lifetime.
• The White House gets a new tenant every few years, but it takes a lot more than money to move in. Hearst Castle is 68K square feet on 123 acres, but I'd put in the honorable mention category because its tucked away in San Simeon, California.
• Putin's Palace looks spectacular, but it's hard to say how many individuals could hope to move in some day.
• Antilia is fascinating and may have cost a fortune, but hard to say how many of the world's richest want to live in Mumbai.
• Chateau Du Champs De Bataille is another property that could be worth 10 figures (located in Normandie France as opposed to the properties below in the French Riviera - video)

Properties in multiple NFP locations

New York

• Ken Griffin's $238,000,000 Condo is considered by many the most valuable property in the United States, but it may not even be the most valuable property in New York.
• Ira Rennert's Fair Field, which was built in 2003 on about 64 acres has a higher assessed value.

Los Angeles

• Jay-Z and Beyoncé's ($190,000,000 or) $200,000,000 Malibu Beach home (built by William Bell) was briefly the highest priced California sale, but was then bypassed by the $210,000,000 sale of James Jannard's Malibu compound (previously owned by Howard Marks & Mark Hughes).
• The Masterpiece is rumored to have cost $300 million to build.
• The 157 acre "Mountain" previously owned by Merv Griffin and Mark Hughes was once listed for $1 billion and reportedly had a $400 million offer. Yet the modestly smaller, but closer to the coast 120 acre Enchanted Hill eventually sold for "only" $65,000,000.

Florida

• Larry Ellison purchased Gemini for $173,000,000.
• But the title for most valuable property in Florida, when it is finished is likely to go to Ken Griffin's Palm Beach development, given that Griffen apparently spent $450,000,000+ to aggregate multiple parcels and homes before starting the redevelopment.

London

• Dudley House was suggested to be worth $400 million in a 2015 Vanity Fair magazine profile.
• 2–8a Rutland Gate (per wikipedia) was sold in 2020 for £210 million, then in February 2023 for over £300M.

France

• Villa Leopolda was contracted to sell for €370 million in 2008 but the deal fell through in the wake of the Global Financial Crisis.
• Villa Les Cedres sold for $220,000,000 and listed for $410M in 2021.
• Château Louis XIV sold for $301,000,000 in 2015 to Mohammad bin Salman.

Hawaii

• Mark Zuckerberg and Priscilla Chan are building a massive compound at Koolau Ranch on ~1400 acres in Kauai, with several articles calculating just the land purchases at $170,000,000+.
• Larry Ellison reportedly purchased 98% of Lanai in 2012 for $300,000,000, including The Four Seasons Lanai, and has continued to invest huge sums of money into the island.
• Marc Benioff has extensive properties on the Big Island of Hawaii (big island) including a 5-acre Mauna Kea Resort estate (see #15).
• Also on The Big Island, Michael Dell owns the "Raptor Residence" and liked the resort of Hualalai so much that in 2006 he bought the whole resort (originally with Rockpoint Group, and later Rob Walton reportedly for over $500 million). His private investment firm MSD Capital was set up to manage his family’s fortune and in 2004 it previously bought the Four Seasons Maui for $280 million,

Ranches

• The Wall Street Journal cites Rupert Murdoch's 2021 $200,000,000 purchase of Beaverhead Ranch in Montana which covers 340,000 acres.
• Even larger and more expensive is Stan Kroenke's W.T. Waggoner Ranch in Texas, at over 520,000 acres (Video). There seems to be some debate about the 2016 purchase price with some citing $725,000,000, but WSJ suggests over $500,000,000.