Saturday, September 29, 2012 is Smithsonian Museum Day, when 20 museums in the Philadelphia area (along with museums across the county) will open their doors for free. A Museum Day Live! ticket is needed for free admission, and can be downloaded here. This event is sponsored by the Smithsonian Museums, which are always free to visit.
Participating local museums include Bucks County Civil War Library and Museum (Doylestown), Brandywine River Museum (Chadds Ford), Penn Museum (Philadelphia), National Liberty Museum (Phila.), National Constitution Center (Phila.), Philadelphia Art Alliance, Rosenbach Museum and Library (where original Sendak drawings and mural, and a Colbert display reside, in Phila.), and others.