Embassy of Indonesia (Walsh-McLean Mansion)

From www.culturaltourismdc.org:

The Walsh-McLean House, a fabulous Beaux-Arts style, 60-room mansion, was built in 1902 for rags-to-riches gold miner Thomas F. Walsh. At the time, it was Washington's most expensive residence. Walsh had the main interior staircase constructed to resemble that found on an ocean liner. Walk to the corner of 21st Street to see the porte-cochere, (literally coach door), where carriages unloaded their distinguished passengers. It is said that Walsh embedded a gold slab in the arch of the main entrance to celebrate the source of his wealth. This was the childhood home of Evalyn Walsh, owner of the “jinxed” Hope Diamond who married Edward Beale McLean, heir to Washington's hometown newspaper, the Washington Post.

As evidence of the neighborhood's rise and decline, it cost more than $835,000 to build this palatial house in 1902 (today's equivalent of over $16 million), and in 1952 the Indonesian government was able to purchase the structure for $335,000.