Horseback riding is very popular in Costa Rica, where the campesino culture depends on the horse for mobility. Wherever you are, horses are sure to be available for rent. (The native horse of Costa Rica is the crillo, a small, big-chested creature of good temperament.)
In Santa Ana (about 9 km west of San José), Club Hípico la Caraña (tel. 506/2282-6106, www.lacarana.com [1]) provides riding instruction.
Scores of ranches nationwide offer trail rides, notably in Guanacaste, where city slickers longing to be the Marlboro Man can pay perfectly good money to get coated with dust and manure alongside workaday cowboys.
Equitour (tel. 307/455-3363 or 800/545-0019, www.ridingtours.com [2]) has 8- to 11-day riding adventures in Costa Rica.
Links:
[1] http://www.lacarana.com
[2] http://www.ridingtours.com