Beijing is really huge and you can’t walk everything as distances are just nuts. The tube is there to help happily and also a horde of rickshas that waits at every possible corner.
The city is a contrast between high towering buildings with village style areas at their feet called Hutongs. These 1 store buildings are usually old and allow ordinary people to live in the city’s center. The local public toilets are very stinky and you’ll be surprised when going for a pee to cross a guy crouching busily in a corner with no shame at all. Streets will offer a mix between local markets but also street food that ranges from ordinary stuff to insects of all kinds.