Unfortunately, nothing quite compares to the rise in elevation like it does in the Himalayas. On the first day of your Everest Base Camp trek, you have to go from Lukla (9,300ft) (airport where you land if you go from Kathmandu, Nepal) to the first camp, which is right below Namche Bazar (11,000ft).

The rise in elevation combined with carrying a 40lb backpack (average), and the difficult terrain leads to levels of tiredness that you can't quite achieve in any other scenario. A lot of it has to do with elevation of course, but the terrain on that EBC trek is absolutely ruthless.

That first day when we got to the first camp, I have never ever in my life been that tired, and even my guide who was with me - advised me not to sleep too much as it will make it worse.

I'm living next to a 1,800ft mountain right now (I'm in Norway) and I can do the roundabout hike in like 2 hours and yeah it stings physically, but it is maybe 1% of what you will feel in the Himalayas.