Northwest of San Jose and north of Alajuela near La Fortuna De San Carlos, the heavily visited Parque Nacional Volcán Arenal has a few nice hiking trail systems.
To reach the trailhead from La Fortuna, head west for 15km. At the park sign, turn left for 2km. From this parking area, there is a 3.4km trail (one-way) leading towards the volcano. Consider exploring the volcano at night to actually see the lava (a guide may be required). Do not try to climb the volcano rim - it is extremely dangerous and people have died attempting it.
Another great spot for trails is the Arenal Observatory Lodge where there are 6km of trails. These are known as the Sendero Los Tucanes and the Sendero Las Heliconias.
The town of La Fortuna is the base for exploring this area. La Fortuna is located about 75km north of San Ramon and about 42km west of San Carlos. The town may have direct air service from San Jose.
Here are some basic notes on driving in Costa Rica for the tourist. There is a myth about the quality of the roads and of VW bus sized pot-holes. This may have been true years ago, but on the main routes, this is no longer true. With that said, there are still numerous challenges for first time drivers in Costa Rica. First, do not expect much out of so-call “highways”, like the InterAmerican Highway. The fancy name makes the uninitiated think this is a major 4 lane divided, restricted access road. Well, yes, about 1% is. The rest is two lane (marginally), undivided, rural roads with tons of traffic constantly stopping, turning, passing or driving slowly. Like every other road in the country, you can expect to see on the road numerous unexpected cows, cyclists, pedestrians, bus stops, school crossing zones, dogs, mud slides, police check points, unannounced one-lane bridges, missing manhole covers, and, of course, a never ending stream of semi-trucks driving erratically fast. What you do not find on any roads is much signage. There are infrequent signs indicating the distance to the next town, and even more infrequent are road names or numbers (if at all), including even within major towns. To make matters worse, signs that used to exist are disappearing due to deterioration or theft. Also, do not expect drivers to use their head lights, even in a heavy rain shower, unless it is really dark. This makes passing in rain a game of roulette since you can't see the oncoming traffic. Speaking of dark, do not drive at night since the roads in some areas can be ruled by those under the influence of alcohol.
If you have to drive through San Jose, make sure to do it at dawn to avoid the horrendous traffic all day long, including weekends. Keep in mind several maps show highways passing through San Jose. This is not true. They end abruptly on the outskirts of town and you have to slug it out in a crazy stop-and-go traffic and many unmarked turns to get to the other side all day long. There are unsigned so-called by-pass routes around San Jose, but finding them can be a challenging game of trial-and-error, and they are only marginally better.
If you have to drive on the Nicoya Peninsula, you can expect to find generally better roads with better signage. However, there are numerous unmarked eroded road sides, especially over stream culverts. do not drive at night. Watch out for the iguanas sprinting across the road.
A GPS unit can be helpful when navigating roads, however, the maps in Costa Rica were created using a special map datum. This datum is not usually available on GPS units but the road base maps were created with it. Therefore if you use the default WGS84 datum with a base road map on the GPS unit, you will always show a position being about 0.5 miles to the north of the road base map.
When picking up a rental car, make sure to check all the tires for wear, check the spare tire pressure, check the tire jack, and make sure to test the lock on the spare tire. It would be wise to quickly purchase a can of Fix-A-Flat.
Overall, Arenal Volcano National Park is the 13th most popular walking & backpacking of all 20 hiking in Costa Rica.