London is an incredible city, with so much to see and do. It is a very walkable city too: it is not as big as you might think and a bit of advance planning will let you link plenty of sights together with a pleasant walk. It’s not all hard concrete pavements, either; green squares and parks abound.
If you still want more tress, then head to the Royal Botanical Gardens at Kew, where you can explore 121 hectares of gardens and botanical glasshouses. Kew was founded in 1759, and declared a UNESCO World Heritage Site in 2003, and with a heritage like that you can explore the place over and over again and still discover something new.
Such beautiful markings, you can see why it got the name.
And ripe for a bit of fun with some photo editing manipulation:
Royal Botanic Gardens, Kew, Richmond, TW9 3AB