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''We skied, rafted and hiked 300km of some of the most difficult terrain on the planet including the Vatnajokull Icecap, lava fields, raging glacial rivers and barren volcanic plateaus,'' Dr Stephenson said.
The toughest part of the trip was ''hauling 50kg of equipment and food and being battered by freezing wind, snow and rain'', he said.
''We completed the traverse with no outside support in 17 days and became the first people to packraft the Skjalfandafljot River from the source to the sea and the first team to complete an unsupported ski/raft traverse of Iceland,'' he said.
His packraft is a kayak-like inflatable raft, about 2.5m long.
Dr Stephenson (38), who is a consultant in the emergency department at Dunedin Hospital, said probably his ''biggest motivation'' for the trip was that ''all the little things that you worry about day to day go away, and you're just left worrying about the really serious stuff''.
''And there's nothing quite like your first shower and shave and the first clean bed sheets.''
This was ''definitely the toughest'' challenge he had faced in more than 20 years of visiting the ''magnetic'' Arctic and in mountaineering trips.
This was partly because of the challenging, uneven terrain, the constantly wet, chilly conditions, and the need to carry heavy equipment, including an inflatable packraft for travelling by river.
But he relished being immersed in remote, ''pure'' wilderness conditions, which could not be fully experienced any other way.
''Fundamentally it's about being in those special places.''
English-born, Dr Stephenson left Yorkshire with his partner, Laura Andrews, and shifted to Dunedin in 2011.
In April 2013 he took part in the Polar Challenge, a 600km race from Northern Canada to the magnetic North Pole, with team-mate and brother-in-law Dr Gareth Andrews and about nine other teams.
Dr Stephenson has just returned to Dunedin after crossing Iceland, again with Dr Andrews, from the Jokulsarlon glacial lagoon on the south coast and travelling by packraft on the Skjalfandafljot River to reach its mouth, at the edge of the Arctic Ocean, on the north coast on May 16.
The Skjalfandafljot River, also known as the River of the Trembling Spirit, is 178km long and is Iceland's fourth-largest river.