If we use the 72 hr transit visa, can we visit the Great Wall from Beijing?

NAK, by using the 72 hr free transit, you can visit the Great Wall. If you stay in a hotel, you don't need to register at the police station on your own, the hotel will do it for you. If you stay at a friend's apartment or somewhere like this, you need to go to the police station in person. The registration only need a few minutes.