BY CAR (~ 5 hours)
First of all, you'll have to rent an off-road vehicle 4 x 4. Limousine or sport cars are unsuitable for Costa Rican roads, which are generally too much rough.
In the
Useful links section, you'll find a list of rent-a-cars you can call for booking. Please remember that, during high season (from Christmas to Easter), prices are generally sensibly higher than during the rest of the year.
During almost all of your trip towards Avellanas you will be using the interamerican (or panamerican) highway.

It's not literally a real highway, since it hasn't a traffic island, and it's crossed by secondary roads. Anyway, in normal conditions it's free from holes, and in Costa Rica this is quite unusual. On the interamerican highway you should pay attention to two things: first, it's highly recommended to respect the highway code, avoinding to exceed velocity limits, travel without security belt or overtake where it's not permitted: the highway is patrolled by plenty of police cars, and you can usually run into two or three subseguent patrols. Second, please be careful of trucks: they go fast, sometimes on the wrong way, trying to overtake slower vehicles.
If you loose yourself, please remember that the interamerican highway runs along the international airport of Alajuela; you can eventually ask Costa Ricans: they are usually friendly (policemen too).
To get to Avellanas, first take direction towards Liberia (if you don't see any signal for Liberia, you can start following the ones to Puntarenas). Always stay in the interamerican highway, without leaving it.
When you reach Puntarenas crossroad, go on for about 50 km, until you'll see,

on your left side, a gas station called "La Irma": after a further 3-4 km, you'll turn left, towards Nicoya and the "Puente de la Amistad de Taiwan" (Taiwan Friendship Bridge).
This bridge links Nicoya Península with the rest of Costa Rica, and it's the only big bridge of the region: you can't miss it. The road that leads to the bridge is generally good, and it's patrolled by police as the highway is.
After the bridge, go on till Nicoya crossroad, but do not enter the city (by doing so, you'll only have a larger journey). Follow directions for Santa Cruz.
When you reach Santa Cruz, you could:
refuel with gasoline or diesel
buy something in a minimarket
go to the post office and send postcards (finding stamps is very difficult in Costa Rica)
change your money in colones, at the Banco Naciónal de Costa Rica (National Bank ok Costa Rica)

Santa Cruz remains out of the tourism ways, so here you'll find cheaper prices compared to other touristic town, such as Tamarindo.
Go back to the main road wich lead you to Santa Cruz, and go on until you leave the town. After a gas station (on your right side) and a small bridge, you'll turn left towards Tamarindo (actually, the crossroad to Tamarindo has no road signs). Here the road turns quite bad, with many holes, so please drive carefully!
On this road you'll also see the first signs for Playa Avellanas: follow them and in about one hour you'll reach Mauna Loa, where we'll be very glad to attend you!
Finally, a recomendation: every time that you stop to refuel, it's a good idea to ask the attendant for an oil and water check. By doing so you'll reduce the risk to have inconveniences.
For further informations about roads and their conditions, you can visit the website of Costa Rican highway police (in Spanish):
http://www.transito.go.cr.
In order to aid you in following our directions, you can download our maps of Costa Rica:
map with road indications (~ 920 Kb)
map without road indications (~ 841 Kb)
giant map of whole Costa Rica (~ 5,05 Mb)