(Messed that up, so once again)
'En rejs' describes a longer journey to a destination and back again, usually thoroughly planned and over multiple days. While 'en tur' is a smaller trip. Or just a walk, for instance.
As someone has already commented, 'among tourists' is a pants translation. This matters because many of the people using Duolingo are not native speakers and so they could learn stupid English from this. It's 'with tourists'.