Irazú and Poás
Irazú and Poás volcanoes can each be visited easily on day trips from San José, with roads that take you to within a few hundred metres of their craters.
Although both are classed as active, they seem content with the occasional burst of steam and gas from their vivid crater lakes.
You'll need a prompt start to arrive at the craters before the clouds roll in for the day, usually around 10am.
Irazú looms above the city of Cartago and at 3432m is the tallest volcano in Costa Rica. It has four dramatic lagoon-filled craters. The main crater is just over 1km wide, with vertiginous walls 300m deep and a sulphurous green lake at the bottom. Be prepared to be blasted by cold winds at the top where the bare pumice creates a moonscape effect. On a very clear morning it is possible to see both the Atlantic and the Pacific from here.
37km north of Alajuela, Poás is a strombolian volcano-a conical shape created by a long succession of non-catastrophic eruptions. Its vast crater is 1320m wide and 300m deep. At the bottom is a circular hot lake. It is reached by a scenic drive from San José, first through a region of coffee cultivation, then through cloud forest. The final walk to the crater is through a stunted elfin forest and areas with little or no vegetation apart from arrayan, a bush with very leathery leaves, and occasional large-leafed 'poor man's umbrella', Gunnera insignis.
Arenal
Arenal Volcano rises in a perfectly symmetrical cone above the town of La Fortuna and its surrounding lowlands.
Arenal is one of the most active volcanoes in the world. It spews almost daily outpourings of incandescent lava, mushroom clouds of gas and steam, and ejects hot boulders that bounce hundreds of meters down its slopes-all helping to ease the pressure deep below the volcano where the Cocos plate is being driven under the Caribbean plate at a rate of 9cm a year.
Arenal is most impressive on a clear night when red-hot lava can be seen flowing from the top of the cone. In the day, ash clouds billow up from the crater and there are dull rumblings from deep within.
The Arenal area is worth stopping for a night or two, there is a good selection of things to see and do:
Hot springs
It is quite common for Arenal to be frustratingly obscured by cloud, but even if visibility is not good there are attractive, popular, open-air thermal baths a short distance from the foot of the volcano where you can relax in warm, sulphurous waters until well into the night, often with the volcano's rumblings as a soundtrack.
Hanging Bridges
The lowlands near to Arenal Lake are blanketed by forests that can be explored on a series of paths and suspended walkways known as 'The Hanging Bridges'. Gently sloping paved trails meander through the shaded forest, opening out at regular intervals on to footbridges suspended over the forest canopy. The views over the verdant canopy, across the valley to the foothills of the volcano in the distance are quite spectacular. It is not uncommon to see families of howler monkeys resting in the tree branches on a hot day, or toucans surveying their forest domain.
Arenal's eruptions
Arenal can be seen very well from a safe distance, but is a real danger to those who venture into off-limit areas. Poisonous gas emissions, ash columns and incandescent avalanches are all regular occurrences and do claim the lives of the foolhardy.
This constant activity is characteristic of a strombolian volcano, and should make Arenal safe from catastrophic eruptions, though it can nonetheless produce dramatic events, the most recent of which was in August 2000 when in a day of thunderous explosions Arenal ejected 20 separate outflows of gas and rock and a 1km high column of ash.
Turrialba
The easternmost of Costa Rica's active volcanoes and one of the largest, Turrialba stands at 3340m and is covered in cloud forest vegetation.
This stratovolcano has three craters at the upper end of a broad, wide summit depression. It is possible to hike or drive up to the rim, where you can walk some of the way around the craters' edge.
Since a series of eruptions in 1866 Turrialba has been quiet, though its steaming craters hint at its explosive potential. Warm rain gear is recommended at the summit, which can often be damp and chilly.
Rincón de la Vieja
Sulphuric vents, bubbling mud pots and fumaroles spatter the dry forests of Rincón de la Vieja National Park, evidence of the volcanic activity underground.
Above it all rises Rincón de la Vieja volcano itself, a 1816m stratovolcano whose 400km² bulk includes nine eruption points, one of which is still active.
South of the active crater is a large freshwater lagoon, Los Jilgueros-a good place for Black-faced Solitaire and Baird's Tapir.