Halloween falls on Tuesday and the epicenter for all things scary on the Island will be William street, where goblins, ghosts, princesses and mermaids of all shapes and sizes go to trick-or-treat. Although William street is the main event, there are many other favorite haunts and neighborhoods where the candy flows freely, in particular Vineyard avenue in Oak Bluffs, which will be closed to traffic on that evening, like the roads around William street too.