Guanajuato was established in a narrow ravine and moving about the city involves, in large part, going either straight up or straight down. There is virtually only one way in and one way out and vehicular traffic in the historic center is chiefly accomplished via a network of tunnels running along the ravine's old riverbed or built into its sides. Pedestrians use a rabbit warren of callejones (alleys) that snake their way up the steep walls of the ravine.