Your first solo trip teaches you that you can figure out a train map, a menu, and yourself.

Travelling alone removes everyone who would otherwise handle the difficult moments, and what you find out is that you can handle them. The train map and the unfamiliar menu are small problems, and solving them yourself changes your estimate of what you are capable of. That revised estimate is the actual souvenir.

Book something short and go on your own, even a couple of days somewhere nearby. Do not over-plan it, since the figuring out is the point. Expect one bad afternoon and let it happen.