About 3 hours from Costa Rica's capital lies one of the most incredible areas on Earth. The Arenal Volcano is located just outside the town of La Fortuna, at the edge of a cloud forest. The volcano erupted several years back and wiped out the town of Tabacon. A series of unusual circumstances during the recovery created a modern day Garden of Eden.
A river flows from underneath the volcano and emerges in a lush wilderness with super-heater water. As the river cascades down a series of natural waterfalls, the water slowly cools. Visitors can go into the shallow river and waterfalls and get a natural Jacuzzi/hot-tub. If you want the water hotter, move upstream...if you want the water cooler, move downstream.
The Tabacon resort has capitalized on this natural phenomenon and created a luxury hotel, swimming complex and spa. There are many small hotels in the area. The most popular is the Tabacon resort (http://www.tabacon.com). The resort features modern rooms, most with a partial view of the volcano. A pool, restaurant, and gift shop. Hotel guests are allowed unlimited free access to the river and pool complex (which is a five minute walk or 1 minute free shuttle ride away). Non-hotel guests are also allowed to use the facilities for a small fee. There is also a free access area along the road, but the river area is not maintained, nor is it as spectacular as it is within the Tabacon grounds.
The hotel I preferred is the Los Lagos resort, located about a 5 minute drive from the river http://www.arenal.net/hotel/los-lagos.htm . The hotel rooms are a bit smalled than Tabacon, however, the rooms all have spectacular views of the volcano and are located about 2 miles from its base. Most of the guests are Costa Rican, but the service was impeccable and the staff speaks English.
At night, every 15 minutes or so, the volcano erupts. From your bed you can see fiery-red sparks and lava flowing from the top and running down the sides...cooling to a brown-red color before melting into blackness...it is an unforgettable sight! The hotel also houses an crocodile farm, butterfly farm, restaurant, pool complex with a great water-slide, and one of the best canopy tours in the country with numerous cable runs through the jungle where you zip past howler monkies and Toucans (in fact, the jungle scenes from the movie CONGO were filmed here). The hotel also has a spa (massages are only $30!) and a hot spring which feeds the pool.
Rent a car in San Juan and drive on the well marked, well maintained paved road for about 3 hours. You should note that almost all cars in Costa Rica are manual-shift vehicles. Beware of the numerous speed traps along the way. Shuttle bus service is also available.