From San Jose, drive to Liberia on the Interamerican Highway (#1). From the main intersection in Liberia (you'll notice the three gas stations and Burger King), drive 5 kilometers north, towards the Nicaraguan border, and turn right at the entrance to Curubande/Rincon de la Vieja National Park/Las Pailas sector.
It is 14 kilometers on a dirt road to the village of Curubande, and another kilometer to the gate at Hacienda Guachipelin.