US buildings have big gapes between their floors?

In these movies, I see people open grids and crawl among the building structure, they enter in a bathroom or an elevator and sundelly are in the penthouse. I was wonder if american buildings are hollow and if so, why don´t they crash? In my country there is no holes in the ceiling, walls or elevators that you can go into, the air condicioning is a machine attached to the wall, you can´t go inside.