In the centre of the city, Victoria Park will have some sort of festival in July -- Folk Festival, SunFest, Rib Fest, etc. You should be able to find a schedule.
If you like parks, visit Springbank Park.
What about the university?
Museums: The Museum London focuses on multiple kinds of exhibits. The London Museum of Archaeology and Lawson Prehistoric Village makes an ideal day trip. Eldon House. Fanshawe Pioneer Village (more for kids).
Did you book downtown and like pasta? Spageddy Eddy's is kind a cool unique place.