Peñas Blancas, 19 kilometers north of La Cruz, [1] is the border post for Nicaragua [2]. Be careful driving the Pan-American Highway, which hereabouts is dangerously potholed and chockablock with articulated trucks hurtling along.
Steel yourself for a very lengthy and frustrating border-crossing process.
The bus terminal contains the Oficina de Migración (immigration office, tel. 506/2679-9025), a bank, restaurant, and Costa Rican Tourism Institute (ICT, tel. 506/2677-0138). Change money before crossing into Nicaragua (you get a better exchange rate on the Costa Rican side).
Transportes Deldú buses (tel. 506/2256-9072) depart San José [3] for La Cruz and Peñas Blancas from Calle 20, Avenidas 1/3, hourly 3 A.M.–7 P.M. daily.
Local buses depart Liberia [4] for Peñas Blancas via La Cruz every 45 minutes, 5:30 A.M.–6:30 P.M. daily.
Links:
[1] http://www.moon.com/destinations/costa-rica/guanacaste-and-the-northwest/the-far-north/la-cruz
[2] http://www.moon.com/destinations/nicaragua
[3] http://www.moon.com/destinations/costa-rica/san-jose
[4] http://www.moon.com/destinations/costa-rica/guanacaste-and-the-northwest/liberia-and-vicinity/liberia