The forest trails are the reason to come to El Imposible. Routes vary by access point and season, but the common thread is steep tropical forest, riverbeds, viewpoints, and a level of quiet that is hard to find in more accessible Salvadoran parks.
Go with a local guide unless you know the current routes well. The park's appeal is precisely that it is rugged; water, sun protection, and realistic timing matter more here than on the polished volcano walks around Cerro Verde.