Zelkova serrata — keyaki in Japanese, sometimes translated as Japanese elm though it is in a different genus — is the principal street tree of central Tokyo. It is planted along Aoyama-dōri, along Omotesandō, along Yasukuni-dōri, in long, evenly spaced rows that as the trees mature form what locals call a tunnel, a tonneru, of high green cover. The Aoyama-dōri row from Omotesandō Station to Aoyama-itchōme — about a kilometer due south — was planted in the 1964 Olympics preparation, which means the trees are now sixty years old and at their fullest. In August at 2 PM, when the central Tokyo sidewalks are returning thirty-eight degrees Celsius of radiated heat, the temperature under the keyaki is genuinely livable.
The picks below run the tunnel and step off it into the smaller streets — Killer-dōri, Minami-Aoyama’s back lanes, the cypress-lined run to Nezu Museum — where the buildings and the secondary plantings hold the cover. The premise is mid-afternoon: the morning is fine in Tokyo, the evening cools quickly, the bad window is from about 1 to 4. Stay Cool grades these against the actual sun angle; in late September the shadow falls farther east and the routes recompute.
A small practical note. Tokyo summer humidity is high and the breeze on Aoyama-dōri, despite the avenue width, is slow. The keyaki shade is necessary but not sufficient. Pair these walks with an ice coffee stop every fifteen minutes — the Blue Bottle on Minami-Aoyama 3-chōme is the obvious one, but the Maruyama coffee at the Spiral building cuts the line.