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I've done Annapurna Base Camp once and Everest Base Camp twice.

EBC's hike itself wasn't terribly hard (except the Tengboche Hill and the Dughla Pass), but the altitude on EBC is brutal ... once you cross 4000m/13000ft you're far above the tree line and altitude sickness becomes a very real threat. The hike starts at 2900m/9300ft in Lukla and base camp is at 5380/17600ft -- big gain, but all of it is steady going.

ABC isn't nearly as high (base camp is at about 4200/13500ft), but the hike starts down at a mere 300m/1000ft -- and you earn every last step of that. The hike is defined by seeing your next town on the ridge over, and realizing you have to hike all the way down and back up a valley to get to it. However, it is so freaking beautiful on ABC that it makes it totally worth it.

I will enjoy that view vicariously. Sounds amazing.