When the weather gets hot...head to the islands!  George's Island and the other harbor islands are a fantastic way to beat the heat.  Bring a picnic or just purchase food on George's.  It's fun to explore the old fort.  You might want to take a flashlight but there is one corner which is more fun to navigate in the dark.  The boat trip out is fun too.  You can leave from Boston or Quincy.  http://www.bostonislands.org/