You can walk anout 140m to Chongwenmen to take subway Line 2 from Tiananmen weat sttaion and get off at Jishuitan. Then walk or take a taxi to the prince gong's mansion .

You can take bus 635 from Deshengmen south station and get off at Zhuzhongchang. Then walk about 210m to the bell and drum tower.
You can also take subway Line 2 and get off at Guloudajie Station, get out of the station from Exit B (southwest exit), and walk south.