My most memorable vacations involve amazing scenery.
At Denali National Park in Alaska, saw the big mountain with no cloud cover. I believe it's the highest mountain in the world from base to top. My first reaction was that's too big to be a mountain.
At Monument Valley in Arizona, my wife and I watched a lightning storm move across the valley, lighting up the stone monuments from behind.
Carlsbad Caverns in New Mexico is the most amazing cavern I've seen, and I'll never forget sitting at the cave entrance at dusk and watching two million bats exit the cave to go out for the night to hunt (took 45 minutes).
Yosemite National Park in California is awe-inspiring. Inspiration Point, Yosemite Falls, El Capitan, Half Dome -- everywhere you turn there's another amazing view.