Camden Market, and Camden Town generally.
Any and all of the London sights, but they are very spread out.
Westminster Abbey, Parliament, Cabinet War Rooms, Buckingham Palace are close. Start at the Palace, then walk down the Mall or through St James’s Park to the War Rooms, then see Parliament by looking up Great George Street, but go down Storeys Gate to visit the Abbey before going to Parliament Square to visit, then cross the Thames via Westminster Bridge to the London Eye. Or reverse. That would be a long day.
Tower of London and Tower Bridge are much further away. St Paul’s is in the City of London between Westminster and the Tower.
West End theatres, but book in advance or visit Leicester Square to see if you can get reduced tickets.
Borough Market near London Bridge is foodie heaven.
The British Museum has amazing treasures and the National Gallery and National Portrait Gallery (take the lift to the top floor and walk down) are my favourites to see the originals of very famous pictures. The galleries are in Trafalgar Square where you can see Nelson’s Column - a mile north of Parliament.
Tate Modern is across a footbridge from St Paul’s. Tate Britain for the Turner collection is in Pimlico.
Fortnum and Masons and Piccadilly Circus are west of here.
This site is good for obscure things:
https://www.atlasobscura.com/things-to-do/london-england
Buy a day travel card or touch in with a bank card for travel on bus and tube. Easiest and quickest way round London.