The garden of Lauderdale House has a sundial that used to be surrounded by 'hours 'picked out in herbs. There is also a plaque with a relevant quote from Marvell's poem, The Garden. I think that since his cottage was so near, the garden of Lauderdale House --which probably in those days included Waterlow Park itself--was the subject of his poem.
in wall of Waterlow Park, Highgate Hill, London, N19/N6?
just beyond entrance to Lauderdale House