Last year I did the last 140km of the Santiago de Compostela pilgrimage in Spain. This stretch starts in the mountains from which you gradually descend to reach the city. Here are a few things I learned from hiking farther in a shorter period than any sane person should. I started light, about 8 km the first day. The second I walked 27. My hardest day was the third, at 35 km, after which the distances to my hostels got shorter 25, 25 & 20 km. Or thereabouts. Now, I'm a fairly fit person. At the time I worked 4 days a week, walking around the store for 8 hours. I also walked to the grocery store, library, friend's houses, etc. And some of those trips could take upwards of an hour - each way. But as 'prepared' as I thought I was, the real deal - walking all day for several days - is different. Here are some things I learned.
1. Blisters come. They're formed by a mixture of heat and friction (ie, if your shoes aren't on tight enough). And they make walking painful.
2. The path crosses little rivults of water all over the place - not rivers or creeks, but rivults of water from rain/ice melt that flow straight down the mountain. This can make the path slippery and you wouldn't want to camp near them.
3. It's cold. I was there in May and we had snow. A blanket under the stars won't cut it when it comes to keeping yourself warm. I was in a building with a sleeping bag and I froze.
4. Carrying food and water makes your bag heavy. You'll unburden yourself of things you packed and REALLY don't need. And you'll discover pretty quickly what things you do and don't need.
5. After several hours of straight walking your feet KILL. Resting for an hour won't help that, it will simply dull the pain for a while. After a day or two sleeping won't dull the pain either. It waits for you to try walking again and then jumps out at you. At that point, the first 10-15 minutes are hellish, after that you almost don't notice the pain - until you sit down again.
6. Not every watering hole has clean drinkable water. And the consequences of drinking unclean water can last for days (luckily I didn't experience this myself though I did come across others who did, and I found a well where the water tasted too metallic to drink safely).
7. (Which is really just a side point of #5) If you start walking at 7am and only take short breaks you can cover 35 km by 4pm - provided you walk quickly (on city streets I can cover 1 km in 10 minutes). Note - though there's still daylight, you'll be in too much pain to walk any further unless someone's trying to kill you, and even then it might not be worth it. By the time I reached Santiago though, the pain had lessened. So maybe seeing a 'learning curve' in fantasy quests would be worthwhile.
8. The more days you walk the less inclined you are to wake up early and start walking again (because you'll be tired and hurting).
9. The more days you walk the more time it takes to cover the same distance. You won't be going as fast the more your feet hurt - but you'll learn the 'one foot in front of the other' chant that keeps you moving, even when you don't want to move anymore.
10. When you get to your nightly destination you'll be too tired to move. Even things as necessary as eating and showering don't seem that important to the all powerful desire to SIT and not move.
11. Gulping water only makes you more thirsty. Take a sip, swish the water around in your mouth, swallow and then take a second sip. This moistens your mouth and makes it seem like you drank more. (Ie, your mouth won't feel dry the way it will if you simply sip or gulp the water.)
12. You can pass all sorts of terrain - from mountainsides, to swampland to one street villages all within a few hours. And shepherds still exist.
13. Hiking in the rain is unpleasant. But so is hiking in heat (due to sweat and blisters), and cold (because parts of you will be hot and other parts freezing).
I'll be incorporating some of this knowledge into my own fantasy writing, and wanted to throw it out there in case others had the idea of making their quests a little more realistic (without wanting to actually go on a quest themselves).
If anyone has questions about my experience, feel free to ask.