You won't be half an hour in Costa Rica before you hear someone say, "Pura vida." Pure life. To ticos, as Costa Ricans call themselves, the expression is "hello," "good-bye," and "I'm fine" all in one. It also sums up the country's biological diversity: In an area the size of West Virginia, Costa Rica houses an outlandish proportion of the world's plant and animal species. Pricey vacation packages abound, but you can skip all that on this nine-day, DIY circuit. You'll bike volcanoes, hike rain forests, and luxuriate in steaming thermal pools. It just doesn't get better.

The charms of the capital city, San José, pale next to just about everything else in Costa Rica, so don't linger upon arrival. Instead, catch a taxi ($4) straight to the Coca-Cola terminal and board a bus ($3.50) bound for the town of Fortuna and 5,358-foot (1,633-meter) Volcán Arenal, one of the world's most active volcanoes. The December-to-April dry season is prime time to ply the area's mountain bike trails. On the half-day tour offered by the Arenal Paraíso Resort and Spa ($65; www.arenalparaiso.com), you'll circumnavigate the volcano, dip down to the blue waters of Lake Arenal, and end up at the thundering, 230-foot (70-meter) Fortuna waterfall.

When it's time to move on, the lodge can arrange jeep-and-boat transportation ($25) to Santa Elena, the gateway to the cloud forests of Monteverde. Spend a few hours wandering a hundred feet up among orchids, bromeliads, and butterflies on six suspension bridges at the privately owned Sky-walk facility ($15; ). The next day, stick closer to the ground on a hike in the Monteverde Cloud Forest Reserve ($12; www.monteverdeinfo.com), where rubber boots are the local fashion. Then grab the 2:30 p.m. bus back to San José. You're headed southeast.

Corcovado National Park may feel unexplored, with its towering ceibas, crocodile-filled rivers, and flocks of scarlet macaws, but well-maintained trails make it the perfect destination for a multiday jungle trek. The 8:30 a.m. Nature Air flight from San José to Puerto Jiménez ($168 round-trip; www.travelair-costarica.com)

GO TO THE LIGHT: The Fortuna waterfall near Volcán Arenal

arrives in plenty of time for you to begin a relaxed, four-day, 30-mile (48-kilometer) hike from the town of La Palma, northwest of Puerto Jiménez, through the park, and on to the village of Carate. You must make camping reservations ($4 a night; +506 735 5036). In Carate, collectivos (microbuses) wait to make the $4, 90-minute trip back to Puerto Jiménez.

Every room at the Arenal Paraíso Resort and Spa has its own private balcony, and they all face the volcano ($65; www.arenalparaiso.com), as do 11 thermal pools. In Santa Elena, the Pensión Santa Elena ($5; +506 645 5051) is a backpackers' hangout near the Monteverde Cheese Factory, known by cognoscenti for its fresh-cream milkshakes ($1.50; +506 645 5150). The Gran Hotel Imperial in San José ($4; +506 222 8463) overlooks the Central Market. In Puerto Jiménez, the Cabinas Los Manglares ($25 and up; +506 735 5002) is as popular with tourists as it is with local troops of white-face monkeys.