I got altitude sickness in Boulder, which is at about 5,000 feet. I felt dizzy and shaky, tired for about 2 days. Then I adjusted to that, but when we went up to Nederland and Rocky Mt. National Park which were 8,000 and 11,000 feet, I was tingling, pale, and sweaty. Breathing wasn't too cool, either. Since we kept going back and forth between these altitudes, it sucked. I did a little ride on one of our last days in Boulder and I was slow. I guess I could adjust, but I definitely will not go on a vacation anywhere at elevation. Who wants to feel sick for almost the whole trip?