Perhaps true in some cases, but I think this is mostly because the area purchased with tax dollars to become public property (state park or national historic site or whatever) is smaller than the area where the battle took place.
The feds picked a couple — Gettysburg and Vicksburg — where they did purchase something close to the entire battle site, and these ARE big.
Jonathan Banks who plays Mike on Breaking Bad and Better Call Saul. He always has a big menacing presence on screen, but then I saw him in an old episode of Dexter, and everyone was towering over him. I went to look up how tall he was, and was surprised to see he is only 5’9". I thought for sure he was 6’+.
But then again a lot of actors are shorter than they appear on screen, like Tom Cruise.
Dealey Plaza, where the assassination of President Kennedy took place. I had seen it in countless photos and television news stories. When I first drove into it, I was shocked at how close together everything was. The distance from the 6th floor window to the car’s position, the distance between Zapruder and car, the proximity of the grassy knoll to everything else all surprised me.
Did you see the Spinal Tap version of it?
When I saw the Leaning Tower of Pisa, I was a bit surprised that it wasn’t very tall. Still impressive, though.
Though I live in a city with the tallest inclined tower, and many skyscrapers, so maybe I’m used to really tall buildings.
He obviously didn’t realize that the main construction at Stonehenge, the ones with the astronomical value, are the real point. The central stones were added 1000 years later and really don’t add anything except bulk. Sir Fred (Hoyle) suggested that they were added to try to propitiate the gods since the astronomical alignments would have drifted off in 1000 years owing to the precession of the equinoxes.
You live in Sao Paulo?
Likewise Antietam, Chickamauga, and Kennesaw Mountain. You could walk all over any of these battlefields, but you’d be committing yourself to several hours to a full day.
Devil’s Tower. Very beautiful and impressive, but not as big as it looks in Close Encounters. 
The first time I heard Tom Cruise stood 3’ 8" I scoffed.
Eh, I thought Montreal’s Olympic Stadium was advertised as the world’s tallest inclined tower. Whether it’s true, I don’t know. But it’s taller than the Pisa Tower.
My penis.
Oh wait,
(Goes back and reads thread title)
Nope…yeah I was right the first time…
If you think your breasts are T-Cups, your expected penis length may have been equally unrealistic.
I’ll add Starry Night to the list of painting that were smaller than you expected.
I once saw a guy walking down the street when I was currently living, and thought “He looks like a short Paul Simon.” I later found out that Simon’s parents lived in that town, and he is 5’2".
I don’t know why, but I never thought he was so small.
I sort of felt like that when I saw the real thing. Everything I’d seen about it on television, etc. made it seem really massive. At the time it was built, of course it was. In modern terms, not so much. Like I said, it could fit in my yard. The taller stones are about as tall as my house.
He had fun with that in the music video he did with Chevy Chase for “You Can Call Me Al”.
The house I grew up in, especially my room.
Arnold Schwarzenegger
When I went to Gettysburg I was amazed at how small some of the uniforms, officers’ uniforms meant for adult men, were.