When finished, the monument topped out at 555 feet 5⅛ inches. At the time it was the tallest building in the world. It is now nearly a foot shorter than that. One of the myths in Washington is that there is a law that no building in the city can be taller than the Washington Monument. There is a height restriction law, but it has nothing to do with the monument. Another myth, which I've spent 25 years telling tourists while working at the U.S. Capitol, is that the color change in the monument was caused by the "great flood of 1856."

under a manhole cover, is a 12 foot high version of it, used as a survey marker.

https://www.atlasobscura.com/places/washington-mini-monument

The old Post Office, now a Trump hotel.

If you look at the enlarged picture of the Washington Monument, you can see the point at which construction stopped and resumed about a third of the way up. Construction of the monument began in 1848, and was halted from 1854 to 1877 due to a lack of funds, a struggle for control over the Washington National Monument Society, and the intervention of the American Civil War.

When construction resumed, they could no longer get stone from the original quarry and that's why there is a slight difference in color between the two sections. When the monument was capped, they used a very rare and expensive metal for the time: aluminum. As this incredible picture I saved from this very website clearly shows:

the monument is 555 feet 5.5 inches tall?