Everything is in the elevation. I'm rather fit, used to be in the army nearly ten years ago. These days I hike now and then. Last weekend I went on a wee tip, 25 km and 1400 m elevation; it took me 9 hours, not including my lunch break. Only carrying water for the day, the said lunch, dry clothes and a bit of gear ; probably a 10 kg pack. Mild weather and decent track. On flat ground, I would have halved that time.

The Atlas mountains doesn't even break 14k feet, and there is no mention of an attempt to summit.

If you're not even carrying your own food/water 18 miles should be a piece of cake.

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.

Nine miles of hiking per day is not gruelling but it's enough to feel like you did something.

I did half-dome in Yosemite many years ago, and if I remember it's about 7 miles one-way with ~4000-5000 feet of elevation change. But the trail is mostly quite good, and it's as much as I'd want to hike in a day.

For a two day trip, especially if the trail is rough, 18 miles sounds about right.