The Maribios chain is the epicenter of one of the most active volcanic regions on earth. Trekking up these volatile giants rewards you with tremendous views from the top, whether you go up there for sunset or camp overnight to greet the dawn. The easiest and safest way to visit the volcanoes is on a guided hike or excursion, arranged by many outfitters in León and elsewhere.
If you do decide to go to the volcanoes alone, it's a good idea to consult park management first. Marena León manages Reserva Natural Volcán Momotombo, Reserva Natural Telica-Rota and Reserva Natural Pilas-El Hoyo, which includes Cerro Negro; Marena Chinandega keeps tabs on Reserva Natural San Cristóbal-La Casita and Reserva Natural Volcán Cosigüina.