This is a unique opportunity to get to know London a little better. For this free (no admission cost) annual event, some of London's most unique buildings and museums are open to the public for the weekend (many of which are normally closed to the public). Many of the buildings have tour guides or volunteers available to talk with you about the building and its history (like Eldon House, London's oldest house). For more information on the different buildings and their locations visit:
http://www.doorsopenlondon.ca/2009/