Although the winding streets and slopes of Toledo's historic center are best navigated on foot, the city's bus networks offer a convenient way of travelling around the outside the city center walls. For travellers arriving in Toledo by train, there is a convenient bus route operating from the rail station to the central Plaza de Zocodover. The UNAUTO company's buses around Toledo are powered by natural gas, and routes operate roughly every 15 minutes from early morning to mid evening. Late evening services are a little less frequent, with final buses departing just before midnight. Single tickets can be purchased from bus drivers, but it is more economical to buy a prepaid bus pass, where trips cost less than half the price of an individual journey. Passes can be purchased from the UNAUTO office next to the Plaza de Zocodover, and can be topped up online, on buses or at the office. Visitors to the historic center who may be little daunted by some of the steep inclines, can take advantage of escalators, located on the east and west sides of the walled center, providing helpful access to the main tourist sites.