Gap Adventures is offering a volcano-hopping stint in Nicaragua. From the site:
Stopping en route for an included trip to see a live volcano in Parque Nacional Volcan Masaya, we travel to Granada—Nicaragua's oldest colonial city. Walk or bike the city’s history avenues to visit the impressive cathedral, the colourful market or archaeological museums. Optional activities include a scenic boat trip or guided kayak excursion among the 365 little islands (isletas) of Lake Nicaragua.
Considering the price, this trip seems pretty darn cool, and at 15 days is actually pretty long for these kinds of tours.