Many people trek to the base camp, just to reach the base camp. That sits about 18,000 feet altitude, far enough below the Khumbu icefall and glacier, and the steep faces of Everest and Nuptse above the icefall so avalanches won't reach base camp... except when the big earthquake stuck a few years ago.
During that quake, Everest's most famous cliff, the Hillary Step, disappeared. It was a 40 foot vertical step of rock on the ridge between the south summit and real summit. After the quake, it was gone. In its place now is a benign steep snow slope with an angle still capable of ejecting a slider off the Kangshung face, into China.
What does it feel like at 27,000 feet? Tie a pillow over your face. Cinch it tight so you can barely breathe. Put 200 pounds of weights in your backpack. Go into a deep freeze meat locker, and exercize vigorously.
At the Cho Oyu summit, which I climbed without oxygen, I coughed chronically with every breath. It took three or four deep breaths to muster up enough energy to take another step. That's me bent over my ice axe, coughing.