Hi Leonard,
You have a couple of options. From the airport you have to get to downtown where all the major bus stations are. You can catch a cab ($20 approx.) or a bus ($2) to get downtown. Once you’re near the La Sabana park or on Paseo Colon get off the bus and hail a cab to take you to the San Carlos bus station on street 12, avenue 7-9. From there you’ll take a bus to La Fortuna de San Carlos from here there are buses going to La Fortuna de San Carlos, which is the major tourist town/transit hub in Arenal. The town itself is about 30 minutes from the lake. The phone number for the station is: 2255-4300.
Alternately, you could catch a public bus to Tilaran, which is on the opposite side of the lake than La Fortuna and about 20 minutes from the lakeshore. That station is on street 20, avenue 3 in downtown San Jose. The phone is 2695-5611. Taxi drivers will know where both these stations are. The trip to Arenal is about 4 hours.
Which town you go to really depends on where you’re staying. I would contact your hotel in Arenal and ask them which is closer to their location.
Third option is a private shuttle, which will cost about $40 one way. There are two main companies: interbusonline.com and graylinecostarica.com. They can pick you up at the airport and take you directly to your hotel in Arenal.
Of course, since the last public bus leaves in the afternoon usually, if you’re flight arrives after that you should get a hotel for the night and catch a bus in the morning. There are several nice hotels right by the airport, with more budget hostels in Alajuela (the town where the airport is) and downtown San Jose. Check TripAdvisor.com for recommendations.
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