An old obsession of mine that I wanted to discuss...
I grew up just south of Allentown, and on a perfectly clear day you can just seen the Philadelphia skyline from the Southern Lehigh public library which is just a few miles west of rt. 309 outside of Coopersburg, PA.
I thought of this as I was looking through some older posts on here about the farthest points at which people could see various cities. I guarantee there is no further spot to see Philly than what I just mentioned.
I always wondered if I was somehow wrong about this, and a number of years ago did some research, finding that the general region of this library is several hundred feet above sea level, well over Philly's, and if you get on a topographical map you can almost draw a line between various hills between the library and downtown philly and prove that you would indeed have a clear line of sight to this.
Anyway, if any of you want more info on this and ever want to check it out for yourselves, feel free to email me at email@example.com
One disclaimer: I don't live in the area anymore and haven't checked this out in a number of years. Hopefully they didn't build any giant structures in the newer development across the street from the library that would block the view.