For me, it would be the first day of a vacation to Montana and Yellowstone in the summer of 1992.
My family was never the outdoor type, so after I'd moved out on my own, that summer I decided I wanted to visit a national park. I picked Yellowstone and few in to Billings, Montana. After I picked up my rental car and started driving towards the mountains, I knew immediately why they call it Big Sky Country.
It was like the entire world opened up to me. The wide open spaces, the Rocky Mountains, Yellowstone...
I still consider that trip to be the single most important life-changing event in my life. It caused me to move sight unseen to Colorado later that year, and I still feel drawn more to Colorado and the Rockies than anywhere else I've ever lived.