Brandywine River Museum offers free admission every Sunday from 9:30am to noon

The Brandywine River Museum, located on Rt. 1 in Chadds Ford, houses a world-class collection of works by Andrew Wyeth, N.C. Wyeth, Maxfield Parrish, and other artists of the Brandywine valley.  It's really worth a look, if you haven't been in a few years.  In addition, there is usually a good temporary display or exhibit to see, such as the highly detailed train display of December, or the Edward Gorey exhibit of a couple of years ago.  Tickets are usually $10 for adults, but are free on Sunday mornings.   On a nice day, you can picnic outside of the museum on the banks of the Brandywine, or walk a long trail that runs next to the river.  It's a pretty sweet deal for something different to do on a Sunday.

For more info about the museum:
http://www.brandywinemuseum.org/mapdir.html