Definitely worth a closer look!
In town, the main sites are just about walkable, but you might enjoy taking the DUKWs tour which covers some of the land sites (at great speed) and then goes into the river itself.
There is a ticket office near the Liberty Bell museum which is also a visitor centre .... you should think carefully about your timings as the visits to the Liberty Bell and the former Parliament building (sorry can't remember its official name) are timed, and timings are adhered to strictly.
There is a trolley bus tour that will take you to the far end of the main street - good for museums. I believe that there is an excellent children's hands-on museum, but we didn't have time to do it. There is a massive food court in the Amtrak train station building/complex, and plenty of nicer places too!
If you are heading out to 'Amish' country, you should try to allow at least 2 days just to hang around. The main centres are Redding, Strasburg (sp?!) and Intercourse (too late, all the jokes have been made!!). Apart from visiting the farmers' markets, there is a great Amish 'museum'/reconstruction (I believe it is near Bird-in-Hand) that is worth visiting to get a close up view of how the Amish live. You can see signs of Amish life all around - not necessarily the horse and buggy transport - but also the large windmills for power generation (supplemented by petrol generators) on farms, and the lack of power cables and phone lines. You may still see the 'phone boxes' on the edge of a property, as it was considered to be against Amish ways to let this 'convenience' control your way of life. There is an excellent book shop called The People's Place in Intercourse - the owner is not actually Amish but has lived amongst them for many years and will be happy to answer your questions. It is not considered polite to photograph the Amish or ask them questions about their way of life. Obviously most people will have seen
Witness and will perhaps base their knowledge of Amish life on that, but the film is quite 'sensationalist', and the Amish have a dignity of life that many of us lack.