In addition to the main routes of a map, you might be interested in giving advanced players additional mobility through an area to avoid obstacles like a sentry nest blocking passage through a particular path. There are many such examples in stock maps, varying in terms of complexity and difficulty. However, you don't want to ruin the flow of your map aesthetically by cluttering it up with invisible clipping and jumbled props. Here's an example: In the above image of an incomplete alpha map, you can assume that through the empty doorways there might be some stairs to climb to the higher level. However, there's another way up as well: by crouch-jumping at the pallet leaning against the wall, a player can then hop onto the light fixture, against the ledge of the window, and then hop across the second light fixture to gain access to the balcony above. Note how none of the props seem "forced" in this example - the fixtures seem realistic and are providing light to the room, and it is conceivable that a pallet might be left leaning up against a wall. Here is a video of a medic performing the jump.