This very active volcano in Guatemala sits only about an hour from the city of Antigua. It is not the walk itself that makes this an extreme trek. In fact, the hike up the slope is relatively easy compared to the other journeys on this list. What makes this an unusual place for a hike are the active steam vents and rivers of lava that run near the trail. As with some of the other hikes on this list, the safest way to walk on Pacaya is with a guide. Aside from the steam and lava, the volcano also emits gases that could prove toxic, so hikers have to be aware of standing downwind of particular vents. Because of its proximity to the city, this is a popular tourist attraction, but people who choose to hire a private guide can easily avoid the crowds and get further up the mountain than casual day-trippers are allowed to go. Travel without a guide, however, is inadvisable because of the many dangers.