With over 6 million artifacts of both world culture and natural history in its permanent collection alone, the Royal Ontario Museum is an establishment on par with the other great cosmopolitan museums of the world. You'll see here extensive fossil exhibits, wonderful examples of biodiversity, as well as symbols and articles of cultural identity that include totem poles, tombs, paintings, and much more. The main entrance is in the new(ish) Michael Lee-Chin Crystal addition, an avante-garde, Deconstructivist design facing Bloor Street West, although there are other entrances in Queens Park. Adult admission is $15; any further information can be accessed at the museum's website.
Note:The ROM also hosts special exhibits like "Wildlife Photographer of the Year," which will inspire you plenty to get back outdoors and continue exploring this varied and incredible world (once you get your money's worth here first, of course).