Tenorio was about 1.5 hours (2 with the construction on the Pan American highway going on then) from Liberia Costa Rica. The final 30 minutes or so is on a hilly dirt road. Four wheel drive is a must! There are actually two entrances. They are only 3km apart by foot, but the bridge inbetween isn’t open to cars yet (as of November 2012), so it is a significant drive. Coming from Liberia, you would certainly enter the way that takes you to the main ranger station.
From Liberia, take route 1 (the Pan American Highway) South (mostly east, there) and then take a left onto route 6 (there should be a sign for Tenorio by that point) and then follow signs to the park. When you finally get to the ranger station, pay $10pp for access to the park.
There is basically one 9km loop. Many people go 3-4km out and back, though we just did the whole loop. It is a very short trip (though down a very long staircase) to a beautiful waterfall. After seeing the waterfall and running back up the steps, you may need to catch your breath for a bit. A little while later is a raised platform to take a look around, but it was pretty cloudy when we were there. Finally, about 3km-4km from the ranger station, you see point where the rivers meet. You have this really cool blue water meeting with the regular river water. Pretty neat (see pic below). From there you backtrack a bit then hit a fork where you can either head back to the ranger station or keep going.
If you keep going, a little while later you will see access to the river. There is a natural hot spring there where you can sit and enjoy (bring a bathing suit and a towel if you don’t want to continue your walk all soaked. You can’t be shy either since there really isn’t a great place to change. The “hot tub” is maybe 10-30 feet downriver from where you hit the river, but it is much easier to find if people are already in it. Look for those with a relaxed look on their faces. The really neat part is that the water on top is very hot, but below is cool from the river water. It makes for a pretty refreshing feeling. There are plenty of hot spring resorts near Arenal that you can pay big money for, or just stop here on your walk.
You then continue your walk through the jungle (it really is a jungle, see the pics). A total of 6km in, you come to a clearing where you are on a short straight path of manicured trees. There is some cool vegetation and some sort of resort there. At that point the fun is over. You continue on to a dirt road and take a left. Follow that for 3km back to your car. Don’t worry there is almost no traffic on that road since the bridge is for pedestrians only.
Tenorio National Park
Entrance Fee is $10pp for foreigners
For more information about my trip to Costa Rica including restaurants and hotels in Liberia and Tamarindo, trips to the national parks, surfing and more, see my detailed Tamarindo Trip Report.