If you want to visit the campus from the west gate, take Metro Line 4 and get off at Yuanmingyuan Station. The west gate is about 100 meters east. Go straight (east) after entering the door, which is the main landmark building in Tsinghua, including the Second Gate and Tsinghua School. Entering the second door is the auditorium, facing the left-hand side of the auditorium, there is a boulevard, along which you can see the I-shaped hall, and you can find the moonlight of the lotus pond (the kind described by Zhu Ziqing) by going northwest. These are the main tourist attractions.
If you want to see the whole of Tsinghua again, there is a campus bus from the west entrance to the first intersection. It's a light gray minibus. Stop when you wave. Off-campus staff is about 3 yuan. This bus will not take the above sightseeing routes, but will walk around the whole of Tsinghua, passing through Zhaolanyuan Community in Tsinghua, East Gate (main entrance, you can see the stone tablet of "Tsinghua University" when you go out), Tsinghua Academy of Fine Arts, and the east and northeast of the gymnasium. You can get off at any time where you want to play, just let the master know. If you are not sure where to go, you can also ask the master where to get off.
If you enter from the East Gate (main entrance), get off at Wudaokou of Metro 13 line, and walk one intersection to the west, you will see the East Gate in the north. After entering the East Gate, if you want to go to the second gate, you need to go straight to the front of the main building (the building facing the door), then turn left (west), and you need to walk some distance to see the second gate.
Ps: Although the west gate is not close to the second gate, it is farther from the east gate. Tsinghua is very big. Please be prepared to walk at least 1 hour. If you get lost during the tour, please ask your classmates nearby.