The National Museum of Natural History
Located across Constitution Avenue from the entrance of the IRS Building, the Smithsonian Museum of Natural History is designed in the same neoclassical style as the Federal Triangle buildings. Part of the 1901 McMillian Plan, which created the Federal Triangle, the museum was built as the first major addition to the Smithsonian, in order to provide space for the growing collections and research facilities. Opened in 1910, the building is the size of 18 football fields and contains more than 126 million natural science specimens and cultural artifacts. Today it is the largest and most visited natural history museum in the world. The museum's National Gem and Mineral Collection originated with the collection bequeathed to the United States by James Smithson of Scotland, along with the money to create the Smithsonian Institute over 150 years ago. The museum is open daily to the public free of charge (Closed Christmas Day).