All of the buildings on Mainstreet are scaled down with each getting smaller from the entrance of MK towards the castle in order to create the forced perspective to make the castle look bigger than it is. That is all the buildings are scaled down except for one, the train station. They did this because the WDWRR uses full sized trains, a smaller building with a large train in front of it would've looked silly
As you walk towards the castle you're actually walking uphill, this is so it slows you down ever so slightly as you enter trying to keep you from running. It is also so as you leave its downhill, which makes you walk just a little bit faster.
Another reason the sidewalks are red on main street is to help you as you read the map. Incase you're too focused on reading the map you'll be able to see that you're on the sidewalk as you stare at your map, and if you see a grayish black you'll know you're on the street.
The cement used on main street (and most of the park) has rubber mixed in with it, so that it will be smoother, unfortunately this is why they can be quite slippery in the rain.
The delicious smell of candy and baked goods you get as you walk down main street are produced by smell machines and pumped through vents.
One of the buildings in liberty square is the old north church, complete with 2 lanterns that illuminate at night
That brown stripe of sidewalk you see running through liberty square is actually the trench they used for their open sewers.
Underneath the haunted mansion is basically a warehouse for MK, complete with boats from POTC and ITASW, and other various junk from around the park.
One from H.S.
Near hollywood and vine on the second floor one of the windows says valiant and valiant detective agency. And there is a silhouette of roger rabbit bursting through the blinds.
If I can think of more Ill be sure to post them