I suggest the following:
1. Summer Palace. The Summer Palace is very big and the dumb valley is very quiet. You can choose to stay there for one day. In spring, you can sit on a bench and watch bloom. In autumn, you can walk on fallen leaves and enjoy the quiet time of nature.
2. Beijing Botanical Garden. Beijing Botanical Garden has a large area, quiet paths and lush flowers, which is very suitable for a quiet day. You can take something to eat, a book, and sit down in the garden to kill time.
3. Beijing Planetarium. The Observatory Park around the Beijing Planetarium is quiet and peaceful, with many trees and few people. If you like binoculars and starry sky, you can spend a quiet day there, observing the sun with binoculars during the day and looking up at the beautiful night sky at night.
4.798 Art District. Although there are many people in Beijing 798 Art District, it is generally quiet, and many quadrangles are quiet. There are many cafes and bookstores, which are very suitable for quiet reading and staring blankly. You can choose to stay there all day.
5. ditan park. Although ditan park is small, it is also quiet and profound, especially on Shuixie Island. You can take a book, have a simple lunch, sit in any corner of the park you like, read, be in a daze, take a nap and spend the whole day quietly.