From San Jose:
You drive the Panamerican Highway # 1 via Palmares, San Ramon, Esparza, towards Puntarenas. You have to get into downtown Puntarenas and follow the map signs to reach the Paquera Ferry Boat. (See map of Downtown Puntarenas#27 and follow the green route).
The ferry ride takes about one and a half hours. Once in Paquera drive towards Tambor and then Cobano. Continue straight through Cobano and follow the signs to Mal Pais.
