Sometimes you can get someone to help you, ask locals. I took my bike into a movie theater once, and the staff put it in the back room for me. I've left it in the visitor center more than once. Every once in a while you'll find a bike locker. Other times, I lock it up in plain sight of a security guard or cop. If it's a sketchy place, I just don't do it. I don't tour much in big cities, though....