Walking up Dartmouth Park Hill in North London, from Tufnell Park towards Highgate, about half way up on your right, you will pass a large grass covered reservoir. The top of the mound is raised above ground level to a height that it is not possible to see what lies behind. The reservoirs (there are actually two) were built in 1855 by the New River Company, for a brief history of the company, see http://www.londongardensonline.org.uk/gardens-online-record.php?ID=ISL019 and are now owned by Thames Water. The main road is on the route of Mike’s currently favoured run 3 or 4 times a week and it was he who noticed the path to the park running the width of the far end of the mound and suggested we take a look. It is not until you reach the end of the path and follow it around that you can see the views … down the steep incline of grass and way out to the South East, over the housing and vegetation of North Holloway in the foreground and beyond, to Canary Wharf, the City, the Shard towering over St Pauls and west to the Post Office Tower just visible over the trees in the panorama above. The first photo is looking back over the reservoirs to the main road.
See London Gardens: https://tinyurl.com/y7r4tmep for a brief history of Dartmouth Park
and two blogs describing the scene before and after the vegetation, home to local wildlife, was removed from the reservoirs in 2012: https://www.andrewwhitehead.net/blog/category/covered%20reservoir