can I Visit Beijing by using the 72 hour free transit?

My plans are to travel from canada to Australia thinking a 72 hour or less stopover maybe in Beijing would be good to experience some culture and sights from that part of the world. Take in some views if the walls and temples. How large is this Administrative area of city of Beijing that one needs to stay in and is there any other prep involved other than being in right line with valid passport when arriving at airport?