http://www.inah.gob.mx/http://www.fodors.com/world/mexico-and-c…During daylight hours, Autobuses México-San Juan Teotihuacán runs buses from Mexico City’s Terminal Norte to the ruins (M$28, one hour) every 15 minutes from 7am to 6pm. When entering the Terminal Norte, turn left and walk to the second-last desk on the concourse. Make sure your bus is headed for ‘Los Pirámides, ’ not the nearby town of San Juan Teotihuacán.
Buses arrive and depart from near Gate 1, also making stops at Gates 2 and 3. Return buses are more frequent after 1pm. The last bus back to Mexico City leaves at 6pm; some terminate at Indios Verdes metro station, but most continue to Terminal Norte
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http://www.lonelyplanet.com/mexico/north…)
A ‘Los Pirámides’/Autobuses Teotihuacan bus departs from Gate 8 of Mexico City’s Terminal del Norte every half hour
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http://www.wordtravels.com/Excursions/?e…)