It's not a building, it's not a sculpture, and it's still a
monument. If you have been to Paris, you have probably walked on it and
you didn't see it. Or maybe you wondered what it was for. It's very small,
but it crosses Paris from north to south. It looks like this:
,---.
/ N \
{ ARAGO } (diameter: 12 cm)
\ S /
`---'
The Arago Monument is made of 135 small brass plates infixed into the
streets all along the Paris meridian, which used to be the standard
meridian in France. The N and S letters mark the north and south
directions.
François Arago was a 19th-century astronomer. In 1893, a
statue of Arago was erected near the Paris Observatory on place de l'Ile
de Sein, where the Paris meridian crosses boulevard Arago, but it was
removed during World War II. In the nineties, Jan Dibbets, an artist
from Netherlands, created this "imaginary monument" as a replacement for
Arago's statue.
I have personally seen these plates at the following places:
in the Luxembourg Gardens.
in the art gallery streets of the 6th district (a dozen of them).
on the banks of the Seine.
in the courtyards of the Louvre Museum, and even inside the
museum.
on boulevard Haussmann.
... and in many other places.
You could find the complete list of locations on the Internet, but of
course it's more fun to go find them in the streets. Just take a map of Paris (like this one) and
draw a vertical line from the Paris Observatory (south of Garden of the
Luxembourg).