There are a lot of different ways to volunteer in El Salvador, and many organizations exist to help. Centro Internacional de Solidaridad (CIS) runs language schools in San Salvador that take English teachers as volunteers. CIS can also arrange volunteer work with any number of political and cultural groups in the country. Green Arrow's Conservation Connection Placement Program, based in Costa Rica, places volunteers in work positions throughout Central America. CISPES (Committee for Solidarity with the People of El Salvador) is a long-standing activist organization affiliated with the FMLN that places volunteers in programs dealing mostly with workers' rights.
Also good for the heart, El Salvador's volcanic terrain provides plenty of opportunities for hiking. You can trek around the rim of San Salvador's Boquerón volcano or follow a trail down into the crater itself. Other nifty hiking spots include the Cerro Verde national park, Montecristo cloud forest and the areas around La Palma and Perquín.
You can catch excellent waves surfing off the beaches of El Sunzal, La Libertad and points west along La Costa del Bálsamo. The islands in the Golfo de Fonseca offer a good excuse to go boating, and you may well encounter dolphins and sea turtles along the gulf's black sand beaches. Rougher waters await down the Lempa, Paz and Torola Rivers, all good for rafting and kayaking. The country's many Turicentros are popular recreational and camping parks usually located at beaches, lakes or natural springs.