How to reach to Beijing Great Wall, Animal Zoo, The cubi Water Building from the city center?

You can take bus to Deshengmen and transfer to bus 919 to Badaling Great Wall(https://www.travelchinaguide.com/china_great_wall/scene/beijing/badaling.htm) .
When go to Beijing Zoo(https://www.travelchinaguide.com/attraction/beijing/zoo.htm) , You can take bus no.27, 45, 105, 107, 111, 206, 209, 319, 334, 347, Yuntong 105, or Yuntong 205 and get off at Dong Wu Yuan (Beijing Zoo) Station.
When go to Beijing Water Cube(https://www.travelchinaguide.com/attraction/beijing/water-cube.htm) , you can take bus 386, 407, 656, 660, 689, 740, 753, 836 (fast line), 939, 944 (branch line), 983 or Yuntong113 and get off at Beichen Qiao Xi Station.