Monteverde is famously hard to reach. There is no airport — the closest are in San José (about 4 hours by road) and Liberia (3 hours). The standard route from San José is by direct shuttle bus or by public bus from Terminal 7-10, transferring in Tilarán or going via the Río Lagarto turnoff.
The last few kilometres of road to Santa Elena are unpaved and badly potholed — a deliberate community decision over decades to slow development. A 4WD is not strictly required but makes the climb easier and quicker, especially in the rainy season. The most popular alternative from Arenal/La Fortuna is the "jeep–boat–jeep" combo across Lake Arenal, about three hours and significantly more scenic than going by road.