Santo Domingo's main attraction is INBioparque, which does an excellent job of not only explaining the country's various ecosystems, but also taking you into them. It's a useful, if slightly expensive, primer before heading out to the hinterlands. You'll wander trails through climate-controlled wetlands and out to tropical dry forest. The forests may not look much different, but your English-speaking guide will explain the subtleties. Along the way, stop at the butterfly farm, insect exhibits, and bromeliad garden. For an extra $3 you can visit the 15 species of snakes housed here in the National Serpentarium. The tour is packed with information—perhaps too much—but if you're visiting Costa Rica for its ecology, it's a worthwhile lesson. An open-air, upscale cafeteria serves typical Costa Rican fare, with a playground within view of terrace tables. The gift shop has a great selection of tagua-nut jewelry and natural history–themed souvenirs and books. Reservations are required for tours.
Road between Santo Domingo and Heredia, 400 m north and 250 m west of Shell gas station, Santo Domingo, 40301, Costa Rica