1.Create a large room and place your player start and a few lights in there.

2.Next create what will be you conveyor belt.

3.Make a 64x64 sized crate and tie it to a func_train and give it the following values

"spawnflags" "5"
"target" "box1"

4.Now place a path_corner at one end of the belt and give it this bit of info, make sure the teleport box is checked on this path_corner.

"spawnflags" "1"
"target" "box1"
"targetname" "box2"

5.And at the other end place another path_corner and give it these values

"target" "box2"
"targetname" "box1"

6.There that wasn't to hard was it :), compile your map and check it out

7. You can also place some target_speaker near the belt playing this sound world/train1.wav

8.Download the example map