The national parks are America's wild playground. Some charge a nominal entry fee, but when you're in, they're filled with fantastic free escapades. Go on a budget-friendly adventure with this particular extract from our money-saving guide, The Best Things in Life are Free.
Vertical hiking at Acadia
The 1.8 mile/3.2km-long Precipice Trail at Acadia National Park dramatically ascends the east face of Champlain Mountain, along super-narrow ledges with vertical climbs up via ferrata-style rungs. Make it: Nps.gov/acad; opening hours vary; $15 individual 7-day pass.
Wild hot-tubbing at Yellowstone
Park on the 45th parallel in Yellowstone and stick to the steam to Boiling River, a bathing spot where hot springs enter Gardner River to produce perfect soaking conditions. Make it happen: Nps.gov/yell; 24hr; $20 individual 7-day pass.
Flower power within the Smokies
More than 1500 wildflowers explode into colour underneath the Appalachians at Great Smoky Mountains National Park during spring. Go backcountry hiking and wild camping ($14 to $23 every night) amid the blooming ephemerals. Look out for black bears. Make it: Nps.gov/grsm; 24hr; free.
Snorkel around a fort at Dry Tortugas
Seventy miles (110km) from Key West, perched on the coral atoll, Fort Jefferson may be the scene of much marine activity in Dry Tortugas National Park. Snorkel round the moat and sea wall, amid fish, coral and wrecks. Make it happen: Nps.gov/drto; 24hr; $5 7-day pass.
Waterfall walking at Yosemite
The best short hike in the epic Sierra Nevada nirvana of Yosemite National Park, this 6.5 mile/10.4km-long trail passes through the thundering mist created by two magnificent cascades: Vernal Falls and Nevada Falls. Make it: Nps.gov/yose; 24hr; $20 individual 7-day pass.
Go bear at Katmai
Few encounters are as exciting as running into a large brown bear within the US national parks. Fortunately, at Brooks Camp in Katmai National Park in Alaska, the bears have tastier fish to fry than you. July-September is the best time to discover their whereabouts. Make it happen: Nps.gov/katm; 24hr; free.
Moon-walking at Great Basin
Two hours' drive in the neon glow of Vegas, the night sky at Great Basin National Park is so clear you can regularly see five planets. Rangers offer free lunar-lit night hikes in summer when there is a full moon. Make it: Nps.gov/grba; 24hr; free.
Theodore Roosevelt National Park, North Dakota (c) Comstock Images / Getty Images
'Hunt' bison at Theodore Roosevelt
Follow in the footsteps of the Conservationist President around the block named in his honor, by going through the badland prairies and fixing a mighty bison in your camera's crosshairs at Theodore Roosevelt National Park in North Dakota. Make it: Nps.gov/thro; 24hr; $15 individual 7-day pass.
Travel through space and time at Chaco
A dark-sky park, Chaco Culture National Historical Park in Boise state broncos has terrestrial wonders to complement its heavenly delights, with 1,000-year-old Puebloan ruins, built to align using the stars during the equinox. Rangers offer free tours. Make it happen: Nps.gov/chcu; 7am-sunset; $15 individual 7-day pass.
