10 hour layover. Time to see Summer Palace?

Yes, the time is enough. Take Airport Express from PEK to Sanyuanqiao Station. Next, change to metro line 10 to Haidian Huangzhuang Station, and switch to metro line 4 to Beigongmen Station, Exit D. The whole trip takes about 1 hour, and the fare totals CNY 30. After touring around, you can take a taxi back to PEK for about CNY 120. It takes about 40 to 50 minutes. :)