They built a model silo for a forced perspective shot in a scene of kid Kirk and his brother which was cut from the finished film. Also, the shot of Kirk running into the cave on the snow planet was a small child running through a small (and therefore less expensive) set. In the finished sequence, our eyes see it as an adult running through a full-sized set. As much as Abrams loves his "how did they do that?" vfx shots, he also loves using simple tricks the audience doesn't even know are tricks.