Yes, historically, walking was the only way to complete the pilgrimage. In the 8th century, Adi Shankaracharya established the circuit entirely on foot, and in the late 1700s, Bhagwan Swaminarayan famously trekked 1,600 km across the Himalayas wearing only a loincloth.
In modern times, most foot pilgrims still use vehicles to reach the base camps but complete the mandatory treks to the shrines themselves. However, a few extreme devotees still attempt the full 1,200 km loop to reconnect with the a
