Paris was a bit overwhelming - large city, lots of people, and so many things to see. One of the difficulties was in deciding what we could reasonably do in the time that we were there. Being first time tourists, we had bought a guide book which suggested starting with a walking tour. On our first full day we began at Notre Dame, then walked across the bridge to the Left Bank and a brief tour of the Latin Quarter. Back across another bridge to the Palace of Justice, which houses the Conciergerie (the prison where those sentenced to execution were held - among them Marie Antoinette) and St. Chappelle - a cathedral where the walls of the main chapel are entirely stained glass. We ended the day at the Louvre, which needed about 4 days rather than the 4 hours we gave it.
I did not realize until we were in Paris the organization of the three 'major' art museums. The Louvre houses pieces from Antiquity and the Greek and Roman eras through the early 19th century. The Orsay picks up in the early 19th century through the early 20th century, and the Pomidou houses the modern collection. There are several other significant museums in addition to these three, including the Orangerie, the Cluny, the Picasso museum and the Rodin museum.
The next day our plan was to see Napolean's tomb and visit the Rodin museum, which is just around the corner, and then to finish our day at the Orsay. Napolean's tomb is located in what was the chapel of the former Ecole Militaire (military school), which also houses a military museum. We thought we would spend from 30 minutes to an hour at the military museum, which has an extensive collection of weapons, equipment, and uniforms from the Chaldeans all the way through World War II. There is also an extensive World Wars exhibit and our 30 minutes turned into 3 hours.
The Rodin museum is a collection of sculptures - mostly works of Rodin, but also works of several of his contemporaries. Several of his works are in a beautiful garden, with the rest in the mansion where he did most of his work. By the time we finished, we were museumed out for the day, and decided to postpone our visit to the Orsay until the Saturday before we left. That turned out to be a less than brilliant decision - we waited in line to get into the Orsay on Saturday morning for more than an hour.
The Orsay is housed in what was a train station. Although not as large as the Louvre, it houses an extensive collection of neoclassical and Impressionist paintings, and really needed several days as well. The Louvre was originally built in the 12th century as a royal fortress and palace for Philip II, and evolved over a couple of centuries into a complex of interconnected buildings. The glass pyramid entrance was built in the 1980's - I got a picture of it, but it does not come close to doing justice to the immense complex of buildings that form the Louvre.