1) The Laugavegur Trail, Iceland
Length: 55km
Duration: 3-4 days
Start: Landmannalaugur
Finish: Thórsmörk
The Laugavegur Trail is a tough-but-rewarding introduction to the Land of Ice and Fire's wild interior. The starting point, Landmannalaugur (180km from Reykjavik), has hot rivers to bathe in. But the trek isn't always so relaxing, taking in a wilderness of black desert, mirror-like lakes, rushing waterfalls, craggy canyons and the mountain ridges of Thórsmörk (Thor's Wood).
"Iceland's oldest geology is younger than Britain's youngest," said Salter. "To walk through this raw landscape, which is still being created and shaped by fire and ice, is to get some sense of how worlds are made."
For those not yet sated at Thórsmörk, the Fimmvörðuháls trail leads an additional 26km south to Skógafoss waterfall and the coast.
2) Mount Roraima, Venezuela
Length: 64km
Duration: 6 days
Start/Finish: Paraitepuy
Iconic Mount Roraima is the highest peak in the Pakaraima chain of eastern Venezuela's tabletop mountains. According to the Indigenous Pemon and Kapon cultures' folklore, the 15km-long and 5km-wide massif is the stump of a giant tree that once provided all the fruit and vegetables for the world. Here, water cascades from the towering cliffs into rainforests that contain plants and animals found nowhere else on Earth, including the Roraima bush toad.
"The sheer sides and flat summit of Mount Roraima are unlike anywhere else on the planet," said Salter. "This triangular ship of rock carries a lost world on its deck."
The trailhead is around 90km from Santa Elena de Uairén, from where travellers can organise guided expeditions. The ascent can be done in two or three days, but Salter recommends taking six to nine days to explore the high plateau, where hikers will find bathing pools at "the Jacuzzis", the Crystal Valley that's filled with quartz, and Maverick's Rock, Roraima's highest point (2,810m), plus the concrete marker where three countries – Venezuela, Guyana and Brazil – meet.
3) Gokyo Lakes and Cho La, Nepal
Length: 130km
Duration: 17 days
Start/Finish: Lukla
"The Gokyo Lakes trek is a cracker," said Salter. "It's a trail to the furthest edges of human habitation, across glaciers, beneath the world's highest peaks, in a landscape of profound spirituality."
Climbing Mount Everest might be beyond the legs, lungs and wallets of many travellers, but this trek that takes in Everest Base Camp is an opportunity to hike through majestic Himalayan mountainscapes.
Starting from Lukla (2,860m), a 40-minute flight from Kathmandu, the route hits maximum altitudes of 5,545m. Hikers will find suspension bridges, river valleys, waterfalls, rhododendron forests, remote villages, Buddhist monasteries and colourful prayer flags as they stay in guesthouses along the way. The trail enters Sagarmatha National Park, a World Heritage Site that contains the Gokyo Lakes – 19 pristine lakes regarded as holy by Buddhists and Hindus – and Everest itself. The Cho La pass (5,420m) is renowned as one of the trek's toughest sections.
4) The Pembrokeshire Coast Path, Wales
Length: 186 miles
Duration: 12-15 days
Start: Amroth
Finish: St Dogmaels
The Pembrokeshire Coast Path (PCP) opened in 1970, with almost the entire length of the trail falling within Pembrokeshire Coast National Park in south-west Wales.
Most walkers start at Amroth, to the south, so the route begins gently and finishes with the more demanding sections in the north, staying at B&Bs, hotels, pubs or campsites along the way.
Highlights of this wild, rugged coast include Saundersfoot harbour, Pembroke Castle, Strumble Head Lighthouse and 13th-Century St Govan's Chapel, with incredible natural beauty in the likes of Barafundle Beach (one of 58 beaches along the route).
"Roman, Viking and Norman invasions left their mark on this coast, as have ordinary people's efforts to make a living from the sea," said Salter. "Pembrokeshire has castles, harbours and beaches galore."
The PCP ends at the village of St Dogmaels. But if you want to keep walking, the PCP is part of the 870-mile-long Wales Coast Path.
5) The Pacific Crest Trail, US and Canada
Length: 2,653 miles
Duration: 5 months
Start: Campo, California
Finish: Manning Park, British Columbia
A true epic, the Pacific Crest Trail (PCT) is the second-longest trail in the US (after the coast-to-coast American Discovery Trail). It runs between the country's southern and northern borders, from Mexico to Canada, passing through California, Oregon and Washington along the mountain ridges of the Sierra Nevada and the Cascades, and up across the border into Canada.
"The crest that divides America's river systems into east and west also ties together the riches of its many landscapes, like jewels on a bootlace," said Salter.
The terrain is fantastically diverse, from desert to snowy mountains, sandstone outcrops to deep blue lakes, pine forests to volcanoes. The PCT also cuts through six national parks, including Yosemite.
Such a massive undertaking requires careful preparation and planning. The Pacific Crest Trail Association provides a compulsory (free) permit, with hikers required to declare a start date.