For more than 30 years Oscar Cadiach risked life and limb to conquer some of the world's most unforgiving terrain, driven by a desire to join the ranks of mountain climbing's elite.   Now aged 64, the Spaniard will finally retire after summiting the world's 14 tallest mountains without bottled oxygen, with his undisputed ascents set to propel him into the record books as the oldest mountaineer to complete a feat achieved by just a handful of others before him.   The quest saw him narrowly avoid plunging to his death. But in July, after three consecutive failed attempts, the Alpine Club of Pakistan confirmed he had topped Pakistan's Broad Peak -- and, some 33 years after he began, he was done.   "It's like a huge burden being taken off my shoulders," Cadiach told AFP in an exclusive interview.   "I have done my part and it's time to retire," he said, adding that he will still teach climbing and plans to publish his story.   A mountaineering instructor by profession, Cadiach was first drawn to the "eight thousander" challenge in 1984 after topping Pakistan's Nanga Parbat, known as the "Killer Mountain" due to the number of people who have died on its slopes.   Cadiach then set his sights on blazing dangerous new trails across the world's highest peaks as a freestyle climber -- without the aid of oxygen or the use of ropes. Mount Kangchenjunga, the world's third highest mountain at 8,586 metres (28,169 feet) after Mount Everest and K2 During an expedition to summit Nepal's Kangchenjunga in 2007, he almost met his demise. Half freezing and weathering 100 kilometre-per-hour (60 mile-per-hour) winds with frostbite, he clung to the mountainside ropeless for an entire day and narrowly escaped falling to his death. "My hands almost slipped off the rock but I succeeded in pulling myself up," said Cadiach. Others on the expedition were not so lucky.   He explained: "It was only after that I realised my friend who was dangling from that cliff with me had fallen and was gone forever."   - 'The best and the worst' - Pakistan's K2 has provided the Catalonian with his steepest challenges, including the loss of his climbing partner Manel de la Matta in 2004. Nanga Parbat, Pakistan's second-highest peak, known as the "Killer Mountain" due to the number of people who have died on its slopes De la Matta died of pulmonary oedema -- a condition when the lungs fill with excess fluid that can be triggered by prolonged exposure to high altitudes -- and was buried at K2's base camp.   "I sat beside his grave before the summit telling him either I would bring him the good news or will stay there with him," he said of his successful 2012 expedition.   "K2 has given me the best and the worst," he explained. "Being on the top of K2 on a full moon night was the best moment of my life, I stood there motionless looking at the stars and the moon and the world below me, it was eternity."   After summiting Mount Everest on two separate occasions, Cadiach says there are stark differences between the challenges posed by the world's highest peak and its second.   "Mount Everest welcomes you, the weather, the climbing conditions, it’s just hospitable," he said.   "It's completely the opposite on K2. It rejects you -- the climbing conditions, the weather, it becomes more hostile as you climb it."   The Barcelona native, who married twice and has three children, says respecting weather conditions and being mentally prepared are important to reaching one of the world's most treacherous summits.   But he also admits that "luck is very important on K2", adding: "Sometimes everything is just together but you still fail because it's just not your moment."   Cadiach participated in 67 climbing expeditions and made 37 attempts to summit the world's eight thousanders before securing his place in the record books.   But after a lifetime conquering the world's highest peaks Cadiach says he feels rather minuscule.   He says: "Being on top of the summit makes you feel great as you look down at the world but at the same time it makes you feel small as you look at the length of the mountain."