Los Ausoles ('the boiling springs') is the surface vent system of the LaGeo geothermal plant — Central America's largest field, supplying roughly 25% of El Salvador's electricity. The BioParque is the safe visitor pocket: bubbling mud, steam vents, fumaroles, and a small on-site restaurant.
Entry is informal — visitors typically pay a few dollars to a local caretaker who walks them down to the active vents. Guides are strongly recommended because the surface crust around fumaroles is thin and the steam is superheated. Sturdy closed-toe shoes only; no sandals.
From Barra de Santiago the drive is about 90 minutes (~70 km). From Caluco, about 45 minutes through Apaneca. Pair with a Ruta de las Flores stop or with Salto de Malacatiupán hot waterfall (also Ahuachapán) for a full geothermal day.