The (US) National Radio Astronomy Observatory likes to say that the Green Bank Telescope is "the largest moving object on land". This was never really true, the fully loaded crawler plus Shuttle and the Rotterdam storm barrier, not to mention Big Muskie, are bigger. But really the largest moving object on lands is the new Chernobyl containment structure. Aren't we proud?
Don't get me wrong, the Green Bank Telescope is an amazing instrument, one of the best in the world, a stunning engineering accomplishment, and a fantastic scientific tool.
I, personally, have used it to find and study a new class of pulsar and to produce what is in some ways the most stringent test of Einstein's theory of gravity to date.
It's also *big*, the dish is 100 m by 110 m and the moving mass is about 7600 tonnes.
@xyzzy they have a rather nice visitor center and tours (though I don't think you get to go up to the receiver room). You might want to bring a film camera (they sell disposables) because digital cameras generate too much interference.
(I cheated, but when I was there they were arc welding all day and running our observations all night so I figured it would be okay.)
@anne visiting this is a bucket list item for me