18 miles is ~30 km (for us, people who use the other measuring system), which, computed roughly, gives me a 6-7 hours walk. Yes, it's expected of a person who goes on trips regularly to see that as a piece of cake but for us, town folks, it might not be that easy, in any case, not a piece of cake.

Agreed, I'd consider myself a very passionate walker but 10-15km a day in hilly terrain is pushing it for me. 30km....maybe on flat terrain.

Of course. I walked four miles in an hour and half for this game called pikmin something but it was in a flat, suburban sidewalk in Colorado. I think most people can easily walk a mile every half hour all day under these conditions. Probably will even be fun if you have someone to talk to along the way.

A trail on a hilly terrain is a completely different story.