29 days and thinking about the oxygen levels!
Whilst the percentage of oxygen stays at 21% as you climb the air gets thinner as the molecules are more dispersed meaning you get less oxygen per breath.
At 12,000ft I will be getting 40% less oxygen than at sea level and by the highest point of the trip I will be getting 50% less oxygen per breath – the question is does that mean I need to be twice as fit?