Azuma Kagami
The name first appears in the Azuma Kagami in 1180. The Kamegayatsu Pass connected the area of Ōgigayatsu (north-west of today's Kamakura station) to Chōju-ji in Yamanouchi (Kita-Kamakura), near Kenchō-ji. Its name comes from the fact it's so steep a turtle wouldn't be able to go up without turning over. It has been declared a historical landmark.