Kamakura's Seven Entrances

The city of Kamakura, Kanagawa in Japan, is closed off on three sides by very steep hills and on the fourth by the sea: before the construction of several modern tunnels and roads, the so-called Seven Entrances (Nana-guchi), or Seven Passes (七切り通し, Nana-kiridoshi) (all artificial) were its main links to the rest of the world. The city was therefore a natural fortress and, according to the Azuma Kagami, it was chosen by Minamoto no Yoritomo as his base specifically for this reason.

Source: Wikipedia — Kamakura's Seven Entrances (CC BY-SA 4.0)