The region is a vast triangle, broad to the east and narrowing to the west. Much of the region is accessible only along rough dirt roads that turn to muddy quagmires in the wet season; a 4WD vehicle is essential. You can descend from the central highlands via any of half a dozen routes that drop sharply down the steep north-facing slopes of the cordilleras and onto the plains. Choose your route according to your desired destination.

Most sights of interest concentrate near the towns of La Fortuna and Puerto Viejo de Sarapiquí. For the naturalist, there are opportunities galore for bird-watching and wildlife-viewing, particularly around Puerto Viejo de Sarapiquí, where the lower slopes of Braulio Carrillo National Park provide easy immersion in rainforest from nature lodges such as Selva Verde and Rara Avis.

Boat trips along the Río Sarapiquí are also recommended for spotting monkeys, crocodiles, green macaws, and other wildlife, and Isla Los Heliconias is a paradise for bird-watchers and botanists.

To the far west, the slopes of Tenorio Volcano and Miravalles Volcano are less developed but coming on strong, with several new nature lodges around Bijagua, one of my favorite regions. To the north, the town of Los Chiles is a gateway to Caño Negro Wildlife Refuge, one of the nation’s prime bird-watching and fishing sites.

The main tourist center is La Fortuna, which is served by dozens of accommodations. Its situation at the foot of Arenal Volcano makes it a great base for exploring; three days here is about right. Numerous tour companies cater to active travelers with horseback riding, river trips, bicycle rides, and other adventure excursions, including to El Venado Caverns. You’ll want to spend time hiking Arenal Volcano National Park, perhaps from the Arenal Observatory Lodge or via a ride on the Sky Tram.

The longer you linger, the greater your chance of seeing an eruption. And there are several hot spring facilities, notably Tabacón Hot Springs, in which to bathe with a stupendous backdrop. Don’t miss Arenal Waterfall Gardens, the most beautiful of garden settings, also with a unique wild-cat rescue center.

Arenal Volcano looms over Lake Arenal, whose magnificent alpine setting makes for an outstanding drive. Windsurfing is a popular activity.

You should allocate up to a week if you want to fully explore the lowlands.