The word covers two quite different things. A working tour is a journey undertaken for the job — a company of musicians moving from town to town to meet a string of engagements, with little leisure in it. A leisure tour is travel for its own sake, to see what is there.
Within leisure travel the word stretches again. It can mean an hour inside a single building — a museum, a gallery, a castle, a cathedral — walked through at whatever pace suits. Or it can mean a long organised trip linking a series of places, usually of historic or artistic interest, often with a guide and a fixed itinerary. The two share a name and very little else.
What has widened is the range of places thought worth touring. Interest is no longer confined to the cultural and the historic: working places draw visitors in large numbers — a factory, a farm, a distillery, a wine estate, a power station, and in several cities the sewers. A tour of somewhere that still does the thing it was built to do is a different proposition from a tour of somewhere preserved, and frequently a better one.