Aside from a skinny circle of coastline and fringing reef, Tahiti is made up of enticing basalt peaks and fern-lined valleys streaked with sky-high waterfalls.

This side of the island is often overlooked and getting into it takes some sweat - so cool off in a few waterfalls and refuel on wild passion fruit. Here are the best places to explore Tahiti's mountainous jungles and how to go about it.

Hire a trekking guide for the Hitiia lava tubes

Lava tubes are giant, elongated tunnels formed by the cooling and rapid hardening of lava. A river runs through these high, dim caves, so trekking through them requires swimming and shimmying over slick rocks in the dark. Hikers carry a torch or wear a headlamp, and going deep into the mossy caverns feels like a journey to the centre of the earth. The first tube is around 100m-long and this leads to a second, 300m-long cave containing two waterfalls whose gushing sounds ricochet through the cave with a hollow drone. The third and longest cave leads to a cavern with an icy cold black lake and yet another waterfall inside. Along the river at the openings between the lava tubes are more waterfalls, and bathing pools surrounded by lush foliage and plenty of sunshine where you can warm up.

Guides in French Polynesia have rigorous training and are generally well-equipped, knowledgeable and professional. Lists of guides are available from Tahiti Tourism and hotels often work with local experts.

Take a 4WD tour to Lake Vaihiria

Four-wheel-drive tours go into the majestic and archaeological-site-filled Papearii and Papeeno Valleys (the island's largest valleys) and up to murky Lake Vaihiria. The jeeps travel on rudimentary dirt tracks (built to access Tahiti's network of hydroelectric stations) and skirt sheer drops overlooking vast river valleys while going up hills so steep you feel like gravity is no longer on your side. These valleys were densely populated in pre-European times and you will see low, stone temples and groups of long-abandoned traditional house foundations. A few rivers have slick natural basalt slides where you can take a break from the vehicle and plunge into natural pools surrounded by ferns and wild guava. Lake Vaihiria is a muddy-green crater lake surrounded by low trees and is more the destination than the highlight. Look for wild raspberries around the shores.

Several reputable operators lead tours to the lake with stops at waterfalls, the river slides, archaeological sites and viewpoints. Most hotels work with guides.

Hike the Fautaua Valley on your own

The best place to independently discover Tahiti's interior beauty is along the Fautaua Valley trail. You will need a $7 access permit from the Papeete Town Hall - a detail that keeps the area uncrowded and pristine. The well-marked trail leads for about two hours through the jungle, full of ginger flowers and wild passion fruit. The first stop is a view of the 300m-high Fautaua Falls. From here, continue another steep half hour to the source of the falls, a smaller waterfall with a natural slide into a deep pool. The pool dumps over the edge to become the vertiginous Fautaua Falls.

The trail starts near downtown Papeete, and the tourist office or the Papeete Town Hall can give you directions. Many hiking guides also lead trips along this trail.

Stay at the Relais de Maroto Hotel at the island's centre

If you are serious about hiking consider staying at the plain and musty - but superbly located - Relais de Maroto Hotel (; rooms from around $85) at the top of Papenoo Valley. From here you can walk to many of the sites included on previously mentioned four-wheel-drive tours as well as more waterfalls, natural slides and archaeological sites. The onsite restaurant serves decent but pricey French fare that you can pair with wine from the owner's vast cellar - the largest in the country.

Go canyoning

For more action, get in a wetsuit and put on a climbing harness for a day of canyoning, which is basically, rapelling down waterfalls. Canyoning is available at the lava tubes, the Papenoo and Papearii valleys and in lesser-known, smaller rivers. Tours usually start with a hike to the top of a valley and from here, expect to be wet all day with waterfalls pounding on your head as you are hung from basalt ledges surrounded by water-refracted rainbows, mosses and watery-green lushness. Warm up around otherwise un-accessible swimming holes over a picnic lunch.

Locations and schedules will depend on the guides. Try the recommended Rando Pacific which will have the most regular schedule.

Celeste Brash is a Lonely Planet author and writer who recently moved to Oregon after 15 years in French Polynesia. She is the co-author of Lonely Planet's Tahiti & French Polynesia travel guide.

The article 'Five ways to experience Tahiti's waterfall valleys' was published in partnership with Lonely Planet.