The Hilton Opéra is actually at Saint Lazare (it used to be the Terminus Saint Lazare and then the Concorde Saint Lazare) so the name is a bit dishonest, but it is still within walking distance to a lot of museums such as the Louvre or the Orsay or the Petit Palais and many others. I wouldn't consider the natural history museum too far to walk because once you reach the Seine, you stop noticing the distance to the next place. However, you might want to take public transportation to return from there, but certainly not a car using a thermal engine.