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If he completes the Big Easy Mountain Marathon at the Snow Farm on Saturday, he will be one of just 70 athletes who have completed marathons on each of the seven continents, plus one in Oceania.
He refers to the feat as the Grand Slam Marathon.
Marcos, with partner Beatriz Rodriguez, set out on his marathon adventure in February last year, running in a Sahara event in temperatures of 35degC.
Six weeks later he was at the North Pole, one of 40 athletes who paid 12,500 ($NZ19,800) to run on the ice in temperatures of -35degC. Since then, he has run marathons in China, Spain, Mexico, Chile and the Antarctic.
A native of Segovia, Spain, Marcos prefers to run on rough mountain tracks and that was the appeal of the Big Easy - the highest mountain marathon in New Zealand, which has 1018m of climbing and 2270m of downhill running.
Doing the grand slam cost about 35,000 but, with sponsorship, he has raised 15,000 for charity.
Thirty runners have registered for the Big Easy marathon and 120 for the mountain bike event, but organisers expect that number to double by the weekend.