The fabulous Canadian travel circus, Cirque du Soleil, in Boston -- and it is well-worth visiting.  Their shows are filled with awe-inspiring tricks and acts, wonderful choreography, excellent music and marvelous staging.  Cirque is one of the great attractions in the world and presents a variety of shows in permanent and travelling venues around the world.  One warning re: Boston.  It is easy to get a taxi to get to the show grounds -- and extremely difficult to get a cab back out. Cirque has a severe design flaw here -- one heard endless grumbling among the people on the way out of the show.  Visitors had to walk more than a mile before they finally flagged down a cab. Big top style touring shows appear in Boston approximately every two years, and arena style shows also visit the Boston area and Worcester.