With a group of astronomers, I went to Llano de Chajnantor, 5100m above sea level in the Atacama, to see the ALMA observatory being constructed. We drove from San Pedro to the ALMA base camp, near the village of Toconao at 2900m above sea level. We had medical tests here, to check blood pressure and oxygenation, before heading on up to the heights. I knew from previous trips to high altitude that I was probably going to feel spaced out and confused, and it turned out as I expected; I felt a little bit out of body by the time we got up to 5100m, hardly able to understand what people said to me and only capable of shuffling slowly across the plateau from the main building to the antennae.
My oxygen-deprived memories are very hazy but I think it was probably awesome. The array is not complete and only about a third of the eventual number of antennae have been installed so far, but it looked incredibly futuristic with all of the dishes strung out across the barren desert plateau. I staggered around and took lots of photos, and occasionally took shots of oxygen from the canisters we'd all been given.