I mentioned Altoona recently. Altoona doesn't have a lot of charms but it was the location of the main workshops for the great Penn Railway and has an interesting railway museum (more about this some other time). It's also close to Horseshoe Curve, which is where the railway climbs up to cross the Alleghenys. Building it was a great engineering feat in the 1850s. It is so important that the Nazis attempted to sabotage it during World War II. The curve goes through 220 degrees and there are more than 50 trains daily on the triple-track mainline, most of them being very long freight trains. The trains climb slowly up the curve, and the ones going in the downward direction are pretty sedate, too. It's a popular tourist attraction, and is accessible via a visitors centre and funicular running to a small park close to the rail tracks. Unfortunately by the time we visited it, steam locomotives had long since ceased to run on this line, but the diesels were impressive nevertheless!