Most of the graphics created for RollerCoaster Tycoon were created as 3D models and then pre-rendered at the correct scale for the game. Many of them contain much more detail than is apparent when you view them in the game, indeed some of the 3D models and highly complex considering how small they appear. Here are a selection of objects from the game shown as large 3D renderings.

Notice the reflections of other objects on the side!

This was one of the last objects to be created for RollerCoaster Tycoon, and probably contained more detail than any other object.

I think this was originally intended to be animated (along with the character on top of the chips/fries stall).

Another large object with loads of detail. Note the lower supports which I think were cropped from the graphic used in the game.

This actually has more detail that you can see, but the unreduced image was a bit large to publish on the internet. Still, you can see the shape of the stonework and arches a bit better in this rendering. 

Not as detailed as the other models here, and shows how you can get away with less detail at the small scales used in RollerCoaster Tycoon.

Complex animation and attention to detail meant this model took longer to create than any other in RollerCoaster Tycoon.

Ruined Church

And finally something different. I think this was created to be used with the spooky or graveyard themeing and was never used in the game.