Besides my mother's face when alive, Niagara Falls.
I cannot just choose one because they all made an impression on me but they were the Grand Canyon, Tabletop Mountain South Africa, Lava flow into the ocean at night in Hawaii, the green lushness of the Philippines jungle/countryside, the point at which the Great Southern Ocean and the Indian Ocean in Australia meet, the red rocked rocky waterhole/waterfall on the edge of the Australian outback, the gigantic waves on the North Shore of Oahu, the beauty of the white sandy beaches at Noosa Heads Australia and the un-ending vastness of the oceans from a ship.