I had school trips in HS, but they were chaperoned, so . . .
Summer after HS, I spent a few weeks at a friend's home in Florida. Her dad was around, but we were left pretty much to our own devices.
The first vacation without parents around, I was twenty, and some friends and I went island-hopping in the Caribbean for a few days. Low-budget, easy-going, and so much fun. Some of the most beautiful beaches on earth. No schedules, no must-dos, just see what happens each day. It was one of the most memorable vacations of my life. Also memorable because I ended up with a terrible sunburn.