The 5.1m (200 inch) f3.3 Hale Cassegrain at Mount Palomar, Southern California:
http://www.astro.caltech.edu/palomar/hale.html and especially
http://www.astro.caltech.edu/palomar/history.html
Solid Pyrex 5.1m reflector built pre WWII, dragged across the country by train then up the 5,600ft mountain on what is still a very narrow, windy road that has ice in the winter. They ground it to final shape there over 4 years, while building the observatory, which in itself is a thing of beauty. (See my avatar).
It was the world's largest telescope until 1993.
Even today you can wander in and take a look at it without a sign of a guard or a question. I've been fascinated with it since I was a young boy.
It was on my bucket list and has now been ticked on numerous occasions.