Like Kalos being based of France, Lumiose City is based of France's capital city, Paris. The Prism Tower is a parody of the Eiffel Tower and the plaza's names are colors in French.
Lumiose City is the largest city in Kalos with 416 inhabitants, and by far, the largest and most populated city in the Pokemon world.
Lumiose City's name may be derived from Paris's nickname, "La Ville-Lumière" which means "The City of Light".
There used to be a glitch where saving in the Lumiose City outskirts would instantly corrupt the save file and freeze the game. If it occurred, players would have to format the save and start over. it was particularly easy to encounter, as unsuspecting players would be tempted to save in what is easily the largest and most disorienting city in Kalos. As a result of this, Nintendo released an updated version of the game to stop the glitch.
If a player went to the second floor of an unnamed building, a supposed "Ghost figure" of a Hex Maniac would come out of the elevator, walk by the player and say "No, you're not the one", before disappearing. This Hex Maniac cannot be encountered again. This has led to a series of Creepypasta videos called the "Lumiose Ghost Girl" with origins of why she is there. Also in Pokemon Omega Ruby and Alpha Sapphire in Mt. Pyre, a Hex Maniac will say the exact same words to the player.