An hour and a half south of Quito, along the Avenue of the Volcanoes, is the dominant image on the Ecuadorian national psyche: the perfectly conical Cotopaxi volcano (altitude 5,897 m, 19,350 ft), claimed to be the world's highest active volcano. Even novice climbers can summit the glacier-topped peak with the help of a good guide, glacier climbing equipment and a hardy jacket. The views from the top on a clear day are incredible. Even so, it's a physically demanding climb, (if not technically demanding, depending on snowfall and current glacier conditions) so proper acclimatization, good fitness and training is essential. A week in Quito or any other Andean town with ample walking and summiting of a lesser peak or two should be sufficient.
Getting there from Quito
The main entrance to Cotopaxi National Park is located just a few kilometers before the town of Lasso. Drive south from Quito for approximately two hours on the Pan American Highway until you see a large sign for “Parque Nacional Cotopaxi.” Turn left (east) at the sign, immediately cross a set of railroad tracks, and follow a dirt road east for 15 km until you get to the Park’s main entrance. Unlike the north entrance accessed via Machachi, the road to this one is relatively well-marked. There is an entrance fee of $2 for Ecuadorians and permanent residents, and $10 for foreign visitors. 
If you don't have your own car, buses run regularly along the Pan American Highway from Quito. Ask to be let off at the entrance and walk or hitchhike to the entrance.  
Many travelers get a kick out of taking the train from Quito. This unforgettable experience costs just under $5 one-way. Ecuadorians have the curious habit of riding on the roof of trains and a small rail is set up around the edge of the bus-looking train to keep passengers from flying off. The train runs Saturdays and Sundays leaving Quito at 08:00 and leaving Cotopaxi at 14:00. The trip takes a little over three hours and takes you o the Boliche recreation area inside Cotopaxi National Park. See the site of the national railways for more information: www.efe.gov.ec
Hiking to Cotopaxi's Refuge
From the entrance, follow the road for about 20 km to a parking area below the refuge. The Park Service has placed signs at most of the key intersections and, unless it’s foggy, you will see Cotopaxi and the road leading up to it on your right.
There is a steep, one-hour climb from the parking area, situated at 4,500 m, to the refuge (4,800 m). If you intend to climb to the peak, it’s wise to settle into the refuge by mid-afternoon as you will have to leave the comfort of your sleeping bag between midnight and two o'clock in the morning.
Summiting Cotopaxi
Though the route has changed over the years due to recession and shifting of the glacier brought about by global climate change, you generally head up the right (east) side of the volcano’s north face to the huge rock wall called Yanasacha, and then the route cuts back left (west), traversing a steep slope to the summit. The ascent along this route, which is usually well-marked by footprints and wands, takes between five and seven hours, and the descent approximately half that time. If there is any doubt about your pace and climbing time, start earlier rather than later, as the snow becomes sticky and difficult to traverse soon after sunrise.
Though not very technical by mountaineering standards, Cotopaxi is not without its dangers. Along the lower section of the mountain you will encounter a number of large crevasses spanned by ice bridges and, just after Yanasacha, you must climb a short but steep, nearly vertical, wall of ice and snow in order to access the final stretch of glacier leading up to the crater.
If you are lucky enough to have a clear, sunny day, Cotopaxi provides dreamy views of the mountainous Andean landscape for hundreds of kilometers in every direction.
Camping Only
For travelers more interested in views of the volcano without actually climbing, there are campgrounds near the train station. For $10 per person ($5 for Ecuadorians), you can have multi-day access to rustic cabins about 400 meters from the entrance. For $5 per person ($3 for Ecuadorians), you can camp out with your own tent along any of the trails around the campground.
Mountain Biking
Mountain biking in Cotopaxi is a spectacular once-in-a-lifetime experience. You descend from the refuge parking lot, cutting through the thin air at bone-chilling speed. Most of the park is, ironically, very flat due to historical eruptions that caused the glacier to melt and form lake beds around the volcano. This is all good news, since riding uphill at this altitude, you could bust a lung - or two.
Other Hikes around Cotopaxi
From the campground, you can access a trail that goes to the peak of Ruminiñahui Volcano (4712 m), a six to eight-hour round-trip and spectacular walk. In reality, walking most any path through the paramo from either the campgrounds or Lago Limpiopungo, towards the ridge to the right of the Southern-most peak of Rumiñahui, will lead you to the peak (the furthest to the left, the South).
There are popular treks that go around the volcano and another, called Trek of the Condor, which starts near Papallacta, passes near Volcan Antisana and finishes at Cotopaxi.
Horseback Riding
There are horseback riding tours for $1 per loop from the entrance to the campsite and back. Along with great hiking trails, you can spot domesticated llamas, wild horses, raptors, Andean gulls, deer and other wildlife.