I visited this WHS in December 2015. I only had a 5-6 hours layover in Philadelphia but I was determined to visit the Independence Hall and the Liberty Bell and try the famous Philly Cheesesteak Sandwich. The Independence Hall is only 15-20mins by taxi from the airport or if you're not pressed for time you can catch a train or bus (30-45mins and cheaper). It was raining quite hard all day when I visited which turned out to be quite a plus point since nobody seemed interested to peek outside the several pubs and eateries. So after visiting the Independence Hall Visitor Centre, I was told to be near the security check and Ranger in 30 minutes time to visit the Independence Hall interior. I proceeded to the Liberty Bell enclosure to see the famous crack bell (it's free!) just opposite the Independence Hall and then headed for the free tour. The tour takes roughly 30 minutes and due to the weather I was lucky to be in a very small group of 8 people. Usually there are 5-10 times as much people so it could get quite crammed. In fact on such days the tour is only limited to the first floor but we got to visit the second floor as well with the steeple, the long room, and the guns room. Most of the furniture is not original except for the highlights: the Rising Sun Armchair or George Washington's Chair, the beautiful organ and a painting illustrating the important people known as single/double/triple signers. The explanation given is very informative and the time inside is just right as there isn't really much to see. Just before you exit the building there now is a brand new UNESCO plaque so be on the lookout. If you happen to visit when there are a lot of people, you can ask one of the Rangers to let you see or take a picture of the plaque and they will kindly show it to you. The exterior is really nothing special either and I felt it this site had a more intangible OUV rather than a tangible one (if any!). If truth be told, it is a great national heritage site but I wouldn't rank it high as a WHS. The mouthwatering Philly sandwiches will surely help you make up for the average site though so go for it!