One doesn't really think of real estate when discussing rare objects. After all, land is everywhere. When it comes to discussing what's "rare" in real estate there are a few distinct categories and despite the old adage, it's not just location, location, location. In fact location is just one of the considerations. When it comes to location, one thing to consider is that the smaller amount of land available, the rarer the land. Property on islands in the Caribbean such as Richard Branson's Necker Island or places like Nantucket, Bermuda, Kiawah Island has a certain rarity just because the real estate available is defined by the shoreline. There's no chance of endless sprawl in these places. Another factor in rarity which also goes under the heading of location is proximity. Nearness to New York City pumps up the prices in the Hamptons, Westchester County and Greenwich, Connecticut.

Sometimes rarity comes down to exclusivity. We see this in the case of private communities where owners pay to be safely tucked behind gates and have access to shared facilities like clubhouses. Exclusivity is sometimes taken to its most ruthless degree when it comes to New York real estate. Getting into one of the famous buildings in New York City such as 740 Park takes not just money but also a fair bit of clout.

What I think makes real estate most rare is history. A piece of real estate that has been lived in by famous people and has a long history achieves a certain level of rarity. The Dakota in New York is a prime example, the list of famous people who have made the Dakota home are as much a part of its value as the building's charm and location. Also under the rubric of history is architecture. For example, in Los Angeles where I live, homes created by modern architect Richard Neutra are worth far more than their square footage and acreage might lead you to believe. A Neutra home owned by Vidal Sassoon recently hit the market for $25 million.

At the intersection of location, exclusivity and history you find some of the rarest pieces of real estate, European castles that are hundreds of years old, villas perched cliffside overlooking the Mediterranean, homes that have their own vibrant character. One of my favorite examples, La Rondinaia in Ravello Italy, was owned by Gore Vidal and is now being turned into a niche hotel. My pick for the rarest piece of real estate currently on the market is Bran's castle, the castle in Transylvania that inspired Bram Stoker's Dracula, which is expected to fetch upwards of $135 million. The rarest real estate is, the kind that almost never comes on the market, it remains handed down in families. For some more of the historic estates on the market check out the gallery below.