Few volcanoes allow you to drive all the way to the rim. Poás does—well, at least to within 300 meters, where a short stroll puts you at the very edge of one of the world’s largest active craters (1.5-km wide). The viewing terrace gives a bird’s-eye view not only 320 meters down into the hellish bowels of the volcano, but also down over the northern lowlands.

Poás (2,708 m) is a restless giant with a 40-year active cycle. It erupted moderately in the early 1950s and has been intermittently active ever since. The park is frequently closed to visitors because of sulfur gas emissions. Over the millennia it has vented its anger through three craters. Two now slumber under a blanket of vegetation; one even cradles a lake. But the main crater bubbles persistently with active fumaroles and a simmering sulfuric pool that frequently changes hues and emits a geyser up to 200 meters into the steam-laden air.

The water level of the lake has gone down about 15 meters during the past decade, one of several indications of a possible impending eruption (after laying silent for 12 years, in March 2006 a series of explosions caused the park to temporarily close). In the 1950s a small eruption pushed up a new cone on the crater floor; the cone is now 220 feet high and still puffing.

The Botos Trail just before the viewing platform leads to an extinct crater filled with a cold-water lake—Botos. The recently opened El Canto de los Aves Trail explores the lake region. This and the Escalonia Trail, which begins at the picnic area, provide for pleasant hikes. The park protects the headwaters of several important rivers, and the dense forests are home to emerald toucanets, coyotes, resplendent quetzals, sooty robins, hummingbirds, frogs, and the Poás squirrel, which is endemic to the volcano.

Oft as not it is foggy up here and mist floats like an apparition through the dwarf cloud forest draped with bromeliads and mosses. Clouds usually form midmorning. Plan an early-morning arrival to enhance your chances of a cloud-free visit. On a sunny day it can be 21°C (70°F). On a cloudy day, it is normally bitterly cold and windy at the crater rim. Dress accordingly. Poás is popular on weekends with local Ticos who arrive by the busload with their blaring radios. Visit midweek if possible.