When Walt Disney built Disneyland in the mid-1950s, he used his knowledge of set design from filmmaking to play tricks on our eyes.
The most famous visual psychology hack is "forced perspective".
It is an optical illusion to make an object appear closer or further (or smaller or taller) through an understanding of space and distance.
You know those goofy photos of people pretending to "tip over" the Leaning Tower of Pisa or "touch the top" of the Eiffel Tower? That's forced perspective and something I greatly regret ever doing.
The most iconic use of forced perspective at Disneyland is the Sleeping Beauty Castle. The lower level is built full-size while each successive level is built to a smaller scale (eg. 5/8ths).
Objects look smaller the "further' they are away. So, the castle's design makes the ~80-foot building look taller than it really is.
Main Street has a ton of examples of forced perspective. Many of the buildings look like 3-story buildings from the exterior, but they are definitely not.
Take a look at the window heights on each successive floor. They get smaller. No normal-sized adult could stand on the "2nd floor" of these buildings. It's because these are 2-story buildings dressed up as 3-story buildings.
My favourite visual trick at a Disney Park has to do with the commitment to keep each world separate.
According to legend, Walt was once walking through Disneyland and saw a cowboy from Frontierland in the Tomorrowland area. He was pissed (fair enough). Every world has to be consistent or the guests would lose the sense of magic.
During the construction of Disney World, the Imagineers made sure that the Tower of Terror — which is taller than other buildings in the park — wouldn't stand out when viewed from Epcot. How? By blending in the design with the Morocco Pavilion (see below).
The trick definitely works, but they aren't fooling me on the *real* height of that tower.