The Musee d'Orsay is housed in a former train station which had to close in 1937 as the platforms were too short for newer trains. It remained empty and was saved from demolish threats after the outcries over Les Halles destruction. So in 1986 this museum opened dedicated to artwork from between 1848 and 1914.
The building itself is quite beautiful and is a perfect backdrop for the stunning artwork inside. What was previous the platforms area is an incredible light and airy space that soars upwards. The gallery is housed over three floors. The platform area on the ground floor is the late 19th century, middle floor is Art Nouveau and painting from late 9th and the top floor. The Impressionist gallery tends to be the busiest part with painting by many of the great artists of this period. However, the gallery is well laid out, so I never encountered any real sense of it being crowded, probably aided by the blank white backdrop to the artwork.
There is a pleasant terrace area beside the cafés which is nice to get a breathe of fresh air and some pleasant views over the city. There are two cafés - the lower one looks lovely, but I just wanted a drink so I picked the self-service café on the mezzanine level. Both cafés have views through the clock face of the building.
It's worth reading up a bit before you go the Musee D'Orsay but not necessary. The museum has a light and fresh atmosphere and has made good use of the space of the former train station. It's a pleasant place to visit and admire the artwork on display without having to tax the brain too much. There are many famed pieces of artwork here, like Monet's waterlilies or Gauguin's Tahitian artwork, but also many other less famed but spectacular works which are probably more incredible due to their unfamiliarness. You could spend a few hours here and cover a fair amount of the artwork with time to linger over a few favourites.
There is an RER stop right at the museum or there are some metro stops not that far away. The Musee d'Orsay is included in the Paris Museum Pass, otherwise a ticket is 7.50 euros, or concessions 5.50 euros, and under 18 are free. It is closed on Mondays, and it opens from 9.30pm to 6pm the rest of the week with late night opening on Thursday.