Walk the South Bank. Start at Lambeth Bridge where you can see Lambeth Palace, with the Museum of Garden History right next to it. Houses of Parliament across the river. Pass by the wall with all the hearts for Covid at St Thomas' Hospital. Westminster Bridge, London Eye, at various points you walk by Borough Market,Southwark Cathedral, Tate Modern, replica of the Golden Hind, oops missed the whole of the South Bank Centre, Shakespeare's Globe and eventually Tower Bridge. At various points lovely views of St Paul's cathedral, and boats going up and down the river while you are at it.
Will that do?