A building whose door is locked or you cannot enter.
Before you can get inside, you must find yourself stuck between something else, such as another wall, or a structure or object, such as a barrel, that is preventing the character from passing over it. (car, barrel, walls, fences, in short, a difficulty that can prevent the character from walking)
Stand in a gap between where you want to get in and the structure that will trap you, in such a narrow space it is normally impossible to crawl on the ground.
Drop an item on the ground (hold the g key or drag it to the ground), then quickly lift it off the ground by walking backward with your fists to block it. (Look at the object on the ground and hold F, but you have to do it very quickly, in a short time after holding F, you must + right click and walk backwards, the character must block with a punch.)
If you succeed, your character will crawl on the ground and you will pass through the walls like butter.