As a backpacker, without the option of leavingmy backpack in a hostel or hotel, are there city lockers where I can lock up my stuff for a day or two,? Valencia for Las Fallas, Cordoba, Barcelona, Seville; London, England; Prague, Czech; were the major cities that concerned me.
Train stations and bus stations are the best places to find lockers and/or left luggage. Usually though, you have to pick up your bags before the end of the day, i.e. you can't leave them overnight.
In London, I believe that all the major train stations have lockers or left luggage. I know for sure that there is luggage storage at St. Pancras, Waterloo and Liverpool Street Station.
In London, they also have lockers at KingsCross station (ridiculously expensive though ) and at Victoria train station. An even better and cheaper option to leave your luggage at Victoria is the bus station as they charge 3 pounds less than inside the train station. In Barcelona I know they have lockers at Sants train station and Barcelona Nord bus station ("consignas" is the spanish word for it). You might even be lucky in the centre at Passeig de Gracia metro.
Hope this helps!
In London most of the major art galleries and museums allow you to leave bags there for free. I know that the Tate galleries and the Hayward gallery are free.
Sure beats having to pay around 10 pounds for the privilege. Problem is that you probably can't leave it overnight. Then again what are they going to do if you don't pick it up? Destroy it? Doubt it. So you could chance it if you need to.
In Seville there are left luggage lockers at both bus stations and a desk at Santa Justa train station. They aren't too expensive either (in comparison to London that is a couple of Euros I think).
Oh and most hostels and hotels let you leave stuff there if you are staying with them so that shouldn't be a problem either.
If you plan to leave your luggage in a train or bus station overnight, read the instructions on the locker carefully. This is what I did not do in 2002 in Munich. The sign was mostly in German, and because I speak very limited German, I read it completely wrong. What I thought was that I was allowed to leave my bags in the locker for 72 hours without a problem, when in reality I was only allowed to leave them for 24, but they would not be removed for 72. So a few hours until my 72 hour deadline I went to retrieve my bags from the locker, and found it locked. Luckily, a nice man who spoke both fluent German and English explained to the German guard my situation and the guard unlocked my luggage for me. He didn't even charge me for the difference ". . . because you're Canadian." which, I've got to say, was reallly nice. You may not be this lucky, though, so read the instructions carefully. You don't want to loose your luggage (though I have no idea what they do with it if you overuse your allotted time).