A memorial to Thomas Jefferson, the third president of the United States. Located in Washington, D.C. The memorial is made of white marble. A spherical dome is held up by columns. Inside the dome is a 19 foot high statue of Jefferson, and inscribed on the interior walls are many of his various quotes.
Jefferson's statue is looking out towards the Washington Monument. Directly in front of the memorial is the Tidal Basin, an inlet of the Potomac River. During the summer, you can rent paddle boats and paddle around on it. Lining the tidal basin are Japanese cherry trees, a gift from Japan in 1912.
The Jefferson does not have as much tourist traffic as the Washington Monument or Lincoln Memorial. It is more out of the way, and less of a famous structure. Early in the morning, it can be a fairly peaceful place to sit; just you, the cherry trees, the tidal basin, and a bit of traffic from the road behind you. It does get swamped every year during the spring, when the cherry trees bloom and everyone comes to look at them.
Some info from the National Parks Service: http://www.nps.gov/thje