Houhai,
Walk 880 meters to Gulou bus station.
Take bus 124, stop 6, and get off at Beihai bus stop.
Walk 430 meters to Beihai Park.
For reference only.
Metro Line 6 takes about 40 minutes, about 3.4 kilometers.
Beihai park,
Walk 1.9 km to Beihai North Station.
Take subway line 6 (direction of straw house), 1 station, and get off at Nanluoguxiang Station (Exit E).
Walk 50 meters to Nanluoguxiang.
or
124 road, the whole journey takes about 40 minutes, about 3.6 kilometers.
Walk 440 meters to Beihai Station (Beihai South Gate).
Take bus 124, 5 stops, and get off at Di 'anmen Station.
Walk 730 meters to Nanluoguxiang.
For reference only.
Metro Line 6 → Metro Line 4. The whole journey takes about 50 minutes, about 14.7 km.
Nanluoguxiang,
Walk 50 meters to Nanluoguxiang Station.
Take subway line 6 (direction of Haidian Wuluju) and get off at Ping 'anli Station.
Change at the station to Metro Line 4 (Anheqiao North).
Take Metro Line 4 (Anheqiao North), 9 stops, and get off at Peking University Dongmen Station (Exit D).
Walk 790 meters to Peking University.
For reference only.
Peking University and Tsinghua are two adjacent universities. Just walk there.
For reference only.