Taking a learning vacation at a national park through one of these nonprofits is a triple winner. The trips are affordable, they help support the parks and expert guides will take you to places most tourists will never see.

Before signing up for a trip, make sure your ability level and fitness match your ambition. Talk to trip leaders before committing to the journey.

ALASKA INSTITUTES

One Alaska Natural History Institutes trip sends participants rafting down the Copper River to learn about geological forces firsthand. Another ferries travelers to the wildlife refuges of the Aleutian Islands. The weeklong Aleutian ferry trip is $1,875 and the five-day rafting trip is $1,475 (1-907-868-8639; www.alaskanha.org).

BIG BEND, TEXAS

Trips with the Big Bend Natural History Association include two-day horse-packing excursions to the Buena Suerte ghost town and a chance to participate in a dinosaur dig with paleontologists for three days. Costs: $425 and $399, respectively (1-432-477-2236; www.bigbendbookstore.org).

GRAND CANYON

Arizona's venerable Grand Canyon Institute has a vast catalog of programs ranging from short day hikes to challenging backpack trips into the heart of the canyon. The four-day "Mule-Assisted Backpack" trip lightens the load by letting participants send 30 pounds of food and gear into (and more important, out of) the canyon on the daily mule trains. $615 (1-866-471-4435; www.grandcanyon.org/fieldinstitute).

COLORADO HIGH

The Rocky Mountain Nature Association supports Colorado's Rocky Mountain National Park with classes that focus on nature studies and art. Courses include a two-day seminar on painting landscapes in watercolors for $150, not including food or lodging (1-970-586-3262; www.rmna.org).

CALIFORNIA SEQUOIA

The Sequoia Natural History Association's class schedule ranges from winter ski and snowshoe outings to summertime backpacking treks that last as long as 10 days (1-559-565-4251; www.sequoiahistory.org).

IN THE SMOKIES

The Smoky Mountain Field School in Tennessee has classes that last a day (wildflower walks for $29) or more (a vigorous five-day trek on the Appalachian Trail is $500). The school also teaches an introduction to backpacking, ideal for beginners. (1-865-974-0150; www.outreach.utk.edu/smoky/).

YELLOWSTONE ASSOCIATION

The association has trips suitable for hard-core backpackers and luxury-loving wildlife voyeurs. The "Learning and Lodging" programs combine nights in a comfy bed at a park lodge in Wyoming with days spent in the field learning about the park's flora and fauna. A three-day stay in spring to learn about the park's bears and wolves will set you back $579, double occupancy (1-307-344-2293; www. yellowstoneassociation.org).