Ometepe ’s twin peaks are a siren’s call for many an intrepid backpacker, and hiking one or both is an intimate way to get to know the island. But do not underestimate the difficulty of the challenge before you: Both peaks are equally dangerous, for different reasons.
Volcán Concepción (1,610 meters) is the more arduous climb, and large parts of the hike are treeless, rocky scrambles. Don’t be surprised if the volcano is off-limits the day you arrive, as Concepción is a quite active volcano, and has spewn gas and ash on several occasions in the past five years, as recently as December 2009. As such, the authorities prohibit climbs when the seismologists show the conditions aren’t safe.
As you reach the volcanic cone, the wind that buffets you is cold until you reach the crater lip, where the volcano’s hot, sulphurous gas pours forth (the clash of hot and cold air is responsible for the almost permanent cloud cover at the top of the volcano). On the off chance the clouds thin, the view from the peak is unforgettable.
Most travelers hike Concepción by way of the towns La Concha or La Flor, and there is an eastern approach from Altagracia  that takes you through an impressive amount of monkey-inhabited forest before hitting the exposed section. Allow a full day for the hike,: five exhausting hours up and four knee-shattering hours down. Take plenty of water, food, sun protection, and good shoes and socks to protect your feet.
Volcán Maderas  (1,394 meters) is more accessible, and the volcano is dormant, if not extinct (in fact, there’s a forested lake within the crater). It is thus more frequently hiked, but remains equally dangerous and is responsible for at least two deaths since 2005.
Volán Maderas is a national park above 400 meters, and for good reason: It’s really beautiful up there. When you reach the crater lip, the final descent down to the mist-swept crater lake requires a rope and should not be attempted without proper safety equipment — make sure your guide packs one.
The most commonly used trail to the top starts at Finca Magdalena ; if you’re not staying at the Finca Magdalena you must pay a trail fee to enter and pass through the coffee plantations. You’ll pass a petroglyph or two  on the way up. The trail, unfortunately, has seen better days. Lack of appropriate maintenance has made a knee-deep mud pit out of much of the upper stretch.
Allow four hours to go up and two or three to come back down, and count on spending an hour at the crater lake (58 minutes of which you’ll spend deciding whether or not to jump in the cold, mushy-bottom laguna).
The other, more strenuous ascent leaves from Mérida. The first three hours are an almost vertical ascent, leveling off into the upper reaches that one hiker calls “enchanted.” Hotel Hacienda Mérida offers this excursion, and can arrange transport back from Magdalena if you choose to descend the other side.
On either peak, a guide is required, and for very good reason: The “trails” as such are unmarked, and branch dozens of times. One death on Maderas was simply an experienced hiker who got lost in the crevices of the volcano’s middle slopes and succumbed to dehydration.
We recommend using a trained guide from the Union Guias de Ometepe (tel. 505/8827-7714, ugometepe [at] yahoo [dot] com, www.ugometepe.com ). Forming a professional collective has enabled the local guides to share knowledge, formalize their training, and get some sharp-looking uniforms to boot. You can hire a guide for $10–20 per group of five people, enriching your trip, giving something back to the community, supporting conservation efforts, and oh yeah, getting back down again safely.