St Mary's stands at the very top of Harrow on the Hill, and its churchyard is the main reason most non-residents climb the hill. The views from the eastern edge of the churchyard extend across the flat rooftops of inner London to Canary Wharf, the City, the hills of Surrey, and on exceptionally clear days to the North Downs of Kent. There are benches to sit on and not very much noise; it is a genuinely peaceful spot fifteen miles from the centre of one of the world's largest cities.
The church itself is largely Norman in origin, though it has been extended and restored many times. The interior has some fine medieval stonework and good stained glass. The churchyard contains the grave known as "Byron's tomb" — a chest tomb where the poet sat as a schoolboy and contemplated the view below. Byron was not buried there (he died in Greece), but the association is real; he wrote about this exact spot in his early verse. The church is usually open during daylight hours.