On my very first job as a real registered apprentice, and I mean this was the first job of the first day, I was teamed up with a journeyman and we set about to pull some wires through some existing conduit that went from one room to the other.
We could only get the fish tape a little over half way through and it would jam. We could see the pipe, this was in a factory and the pipe was run on the surface. And it was a straight line from one room to the other.
Or so we thought. We messed with this for hours. The j-man tried every trick in the book and he knew lots of them. So it was decided we were going to have to cut the conduit to remove the obstruction. So, we used the fish tape to measure the length from the box to the obstruction. Upon measuring it appeared the obstruction was in the other room. So we went to the other room to do the same thing so we could mark the area we had to cut. Hmm....the two measurements overlapped by several FEET.
The j-man gets a funny look on his face and gets a shop person to move a huge cabinet (it took a small fork lift) away from the wall. Behind the cabinet, which was only inches from the ceiling tall, was a box and a receptacle. The box had two pipes. One from one room, and one from the other, running into the top. The cabinet obscured the two pipes running down the wall from view and it looked like it was just a single pipe running from room to room.