The Louvre sits on the right bank between the Tuileries and the Pont des Arts. Palais Royal–Musée du Louvre on the 1 and 7 lines is the direct stop; the passage under the pyramid is the default funnel. Timed tickets. The building is a former royal palace around a courtyard, with I. M. Pei’s glass pyramid (1989) as the new door. Pick a wing. The Denon wing holds the crowd magnets. Richelieu and Sully are where the palace still feels like rooms.
From fortress to public museum
Philippe Auguste built a fortress here in the 1190s. The medieval foundations are still in the basement circuit. Francis I started turning it into a Renaissance palace; Henri IV and Louis XIV extended it until the court left for Versailles in 1682. The Revolutionary government opened the Grande Galerie as a public museum in 1793. Napoleon filled it; later regimes kept filling it. The Arc de Triomphe du Carrousel in the garden is his, and so is the habit of treating the collection as a statement of the state.
The Mona Lisa is a small portrait behind glass in a packed room. The Winged Victory of Samothrace sits on a stair that was designed for her. The Venus de Milo has her own alcove. None of these three is the museum. The museum is Assyrian reliefs, Dutch galleries you can actually stand in, the apartments of Napoleon III, and a moat. The pyramid was hated, then adopted, then used as a logo. It works as a meeting point. It is a bad place to start looking at art.
Why it is the most visited museum
People come because it is the Louvre: size, the three famous objects, and the fact that a palace is more photogenic than a purpose-built gallery. It is popular to the point of injury in high season. Wednesday and Friday late openings help. The first hour on a weekday in November is a different building from Saturday at 11.
The Tuileries outside are the decompression. The Cour Carrée at night, when the museum is closed, is still the architecture. You do not need a ticket for that.
If you go
Book a slot, enter by the Palais Royal passage or the Carrousel if the pyramid queue is a show, see one thing you came for and one gallery you did not. Do not stack the Louvre and Versailles on the same day. Paris already has Orsay for the nineteenth century and a lot of smaller museums that still have air. Leave through the gardens, not back through the shop spiral if you can help it.