Few active craters can be seen this close and this easily. A paved road leaves you almost at the rim of Poás, peering into a 1.5-kilometer crater with a hyper-acidic turquoise lagoon steaming at the bottom. The smell of sulfur reminds you the mountain is alive. Get there early: in the morning, before the clouds roll in, the view is total. One of the most accessible volcanoes in Central America.