I'll spare you assorted conjecture on why the designers of this city decided to place Masonic symbolism all across the landscape on a scale that can be seen from space. Just take a look.
The dividing street right down the vertical center of this satellite image is 16th Street Northwest. Across the top of the inverted pentagram is "P" Street NW, leading from that little hooked bend in Rock Creek to the right, through Dupont Circle. At the southeast corner of the intersection of 16th and "P" Streets NW is the Masonic Temple, which is quite the imposing if somewhat blocky building, guarded by two definitely-imposing Sphinx, which face the west. To the west of 16th Street, the neighborhoods are generally pretty good. But behind the Sphinx' backs, life gets pretty ugly pretty quickly. At the intersection of 13th and "P" Streets NW, the upper right-hand corner of the inverted pentagram, life is less that pretty. This was, however, once a very fashionable neighborhood, and Logan Circle itself is graced by many fine mansions - but I wouldn't want to be there after dark without a clear mission.
The rightmost point of the inverted pentagram of the old downtown is Mount Vernon Square Park, which lies at between 7th and 9th Streets NW, athwart two of the internal divisors of the pentagram, New York Avenue and Massachusetts Avenue. Massachesetts Avenue continues on to the southeast to the lovely if dangerous Lincoln Square Park in Southeast Washington, also graced by many former mansions mostly now converted to business uses, primarily assorted tax-free membership organizations and political action committees. Lincoln Square Park is not a good place to loiter after dark, though. It's also the easternmost point of a pentagram which lies on its side, pointing east, with the topmost point located at 6th and U Streets NW, with the southernmost point at the juncture of the Washington Channel and the Potomac River with the two westernmost points at roughly the Pentagon in Virginia and Sheridan Circle at Massachusetts Avenue, 23rd and "R" Streets NW.
The westernmost point of the Great Inverted Pentagram of Washington DC is George Washington Circle Park located at the intersections of "K" Street (an internal divisor of the pentagram), New Hampshire and Pennsylvania Avenues, and 23rd Street NW. The bottom point of the pentagram, some would say the focus, is the great obelisk known as the Washington Monument... or is it? Look again.
Some say that there is a smaller inverted pentagram implied but not implicitly delineated within Lafayette Park, to the north of the White House, just across the street. It can also be noted on a slightly larger map that were the "missing" street between Logan Circle and Mt Vernon Square extended southeast, it would neatly intersect the Capitol building. With a little imagination, one can discern other pentagrams-within-pentagrams.