Hampstead Heath is London’s coolest summer walk in the literal sense — its ancient oak woodland (Kenwood) and the chain of ponds drop ambient temperatures 3 to 5 degrees vs the city below. The village itself sits between the heath and Belsize Park; the lane geometry is older than the grid and the upper-floor jutting catches the sun for the streets to keep.
These three pair the heath’s shaded approaches with the village high street. We avoid Hampstead’s open meadow at noon — full sun. The cool walks are all in the woodland.