Good book for a Europe trip?

Hey everyone, I'm going on an 11 day trip to London, Paris, and Barcelona and although I know I will be VERY busy I still want a good book to read in my down time (on trains between cities ect.) but I don't know what to pick? Let me know your suggestions for a type of book about a euro adventure or something of that nature, preferably containing one or most of the cities I will visit. Thank you so much! =)