If you only had a day in Paris, most likely you'd see the Eiffel Tower, pass by Notre Dame (the outside only, post-fire), and maybe try to squeeze in the Louvres, or the Musee d'Orsay. But there's an alternative: Your tour bus could visit the pharmacy at Place Monge so you could buy shampoo. That's what an awful lot of tour groups, especially Chinese and Korean, do on their one day in Paris, during a six-countries-in-one-week whirlwind European tour.