I'll be arriving in Milan, Italy by train from Rome around 12:00 and have to leave for the airport at around 21:00 the same day. I'm with my family of 4 and thought of booking a hotel room essentially just to keep the luggage there and to use the WC.
Do you think it would be possible to book just a single room for that purpose? Or that the Hotel would frown upon it?
Milano Centrale station has a [left luggage office(http://www.milanocentrale.it/en/service/detail/left-luggage1); for 9 hours the fee is €7.80. There are of course toilets (with a €1 fee), but unfortunately no shower. It seems that there is a wifi hotspot too, I can't find any information as to whether it's free.
While there are hotels in Milan with day rooms, you'd have to vacate the room by 18:00 at the latest. It doesn't seem worthwhile unless you really want to sleep.
It would really depend on the hotel, and their terms and conditions. More than likely, you'll probably be charged for a full night as the hotel will find it hard to sell the room once you all depart.