In Haidian, east of the New Summer Palace (Yiheyuan) you can find the Old Summer Palace, Yuanmingyuan. Both Palaces were destroyed during the second Opium War. The New Summer Palace was rebuild, the Old Summer Palace remains a ruin, a memorial. Stroll around beautiful gardens, visit the ruins oft the European Style Palaces. Get lost in a maze. Admire the lotus in the lakes.
If you do not get here by car/Didi/Taxi, take Subway Line 4 and get off at Yuanmingyuan. Take exit B and you can see the entrance (south gate).
More infos: https://www.travelchinaguide.com/attraction/beijing/yuanmingyuan.htm