No direct bus service. Easiest way is to take a car or take a cab (which are available at the hotels). By bus, quickest way is to take bus to MGM and then walk over to BW or take boat to BW. Other option is plan to spend part of day in Epcot, go there and then walk over to BW via the International Gateway exit near United Kingdom. If you leave BW late after parks close, highly recommend cab because otherwise you need to bus to Downtown Disney and catch AKL bus there.