Atenas is about 40 km west of San José, an easy drive on the Autopista del Sol (Route 27). In light traffic the journey takes around 30 to 40 minutes; in San José rush hour it can stretch to an hour. There is no train service.
By bus, TUAN runs regular departures from the Coca-Cola terminal (Terminal Coca-Cola) in San José. The journey takes around an hour and drops you at the bus stop on the central park. Buses run roughly every hour during the day. The fare is inexpensive — under 1,000 colones as of writing.
If you are arriving from Juan Santamaría International Airport, the airport is directly on the Route 27 corridor and Atenas is a straight shot west with no need to pass through San José city centre.