How do I get to summer Palace from Chongwenmen station & return by subway? How long?

From the Summer Palace, you can take the local subway line 2 to reach Xuanwumen Station where you can change to line 4 to reach Beigongmen Station. Get out of the station, you can find the summer palace. The journey takes about an hour and a half to two hours.
Get out of the Beigongmen Station from Exit C or D, you can walk to that entrance in about several minutes. You can go back from the Beigongmen Station and go back to Chongwenmen in the same route.