Yikes! I have so many!
Hitchhiking on the back of a truck on my own from Wadi Halfa to Khartoum across the Sudanese desert was hard, but special. Climbing up Mount Fuji in darkness to arrive at daybreak. Chugging down the Mekong from Luang Prabang In Laos on a little boat with my hubby and friends. Hiking the Milford Track here in New Zealand with four other families and all our teenage children.
Probably the best memories are as much about the people you are with, as they are about exotic locations.