I have heard from several people who do not use GPS and are interested in these alternatives. I am a very low tech and a very cartographically challenged person, but Here are my thoughts:
1. Alpinista route from Irún to Pasajes. So long as you find the turnoff after the sanctuario, which I did without a GPS, there is no problem. Very well marked.
2. Pasajes to San Sebastián. There is a spot along the coast where the Camino tells you to ascend, and there is a sign for the GR 121. Stay on the GR121, absolutely. The Camino, I've been told, is asphalt on that stretch, while the GR is lovely and dirt. Well marked.
3. Zumaia to Deba. This is a very well known route, called Ruta del Flysch. It is gorgeous, a bit strenuous, and well worth it. Everyone in Zumaia can get you to the starting point and from there the marking is good into Deba. I continued on to Izarbide and stayed with Nerea in her great albergue (has had some problems recently but that was only because she had sublet the place to someone while she cared for her dying brother and she is back). Some may find that too long a stage and can easily shorten it by staying in Deba.
4. Castro Urdiales to Laredo. This alternative is well described in the document, I think, and it is for the most part the official camino. It's just that a lot of people decide to take the "straight shot" along the highway. I get why you would do that if the weather is bad or you are in bad shape, but otherwise, the coastal route is the way to go, IMO.
5. Santander to Boo. This route hugs the coast out of Santander. It involves a loop, so you may think you are headed in the wrong direction. This route has been extremely well described by Dave (author of Northern Caminos) both online and soon in the new version of his Northern Caminos book. So I am fairly confident you can do it without GPS if you are good with maps and directions. It was as long day to Boo, I think I arrived around 4. 38 maybe?
@Nuala recommends breaking it up at a point in the middle, in the very nice hotel rural that is there. Contact them ahead of time if you plan to stay there. And it's likely to be easier to get a room there in off-season.
6. La Franca to Llanes. Without a GPS, I think it might be hard to find the trail right at the place where I started. But as WisePilgrim explained to me, and his guide describes, there is a point on the main national highway soon after leaving La Franca, where you will see very clearly a trail off to the right. It will take you straight out to the coast, and I THINK may involve crossing the FEVE tracks. This is the stretch where the "natural stone bridge" that Amancio described. It is not a terribly long crossing, and it is plenty wide, but the rocks are extremely, well, rocky. If this may be an issue for you, you can stay on the highway till Buelna and from there make your way straight north to the coast. It will be obvious, because I could see Buelna nearby from my coastal path. This is also a long day, and could be shortened by stopping in Pendueles. This was probably my latest arrival time, I think it was around 3 or was it 4.
7. Llanes to Playa del Poo and beyond. It's easy to start out of town on the coast, both Dave and WisePilgrim tell you how. I confess that I am a little confused about where Play del Poo is and where I actually walked, but it was a really nice coastal walk that must have been the E-9. That means that locals will be able to help you. This was a route with lots of people out walking dogs and waking with friends early in the morning. Not the most spectacular, IMO, but very pretty.
8. After La Nueva to Ribadesella. I walked Llanes to Ribadesella with options 7 and 8 in the same day. Others might want to break it up, and La Nueva is one good place to do it. There is a nice little two star family owned hotel there. This was one section where I was glad I didn't have to figure out how to get to the coast. My GPS had a direct route from the Camino someplace after La Nueva. Talking with the people in the hotel where I had my coffee break, it would be very easy to get to the coastal route directly from La Nueva. Without a GPS, this might make the most sense, but of course it would add kms. There is a sign in La Nueva directing you to the "playa." I would probably do this if there is a next time for me. Adding a few more coastal kms and spending the night in La Nueva would make a good day into Ribadesella.
9. and 10. are not coastal routes at all, but they are both alternatives that I HIGHLY recommend.
11. Soto to Cadavedo. The higher route is well marked as an alternative on the Camino. Another highly recommended option, and no GPS would be necessary.
11A. Barayo to Navia. I learned of this option only after
@Kosmos posted about it. There is a lot of information earlier in this thread. Leaving from either Luarca or Otur in the morning should make for a nice coastal day into Navia, which is a big town and must have a lot of places to stay. I have no idea about the feasibility without a GPS though.
12. La Caridad to Ribadeo. This is another one where the official camino markings give you a "coastal option" through Tapia or a shorter shot that stays on the road. What I found, though, was that my GPS tracks actually took us to beaches along the coast that the Camino did not pass. I note the spot at which the Camino does merge with my coastal GPS tracks, but there were some stunning spots before the merge that we thoroughly enjoyed, actually getting down and into to the water several times. I suppose it is easy to find the trail by just forging north to hit the coast after Tapia, though, so this would be one where you could add the coastal kms without worrying or needing a GPS.
Rest of the suggestions are not coastal at all, and all are marked. If you can find the higher route out of Mondoñedo, you are smarter than I, because I tried three times and kept finding myself on the old camino route. Ignore what the hospitalera in Lourenzá says, this logging road out of Mondoñedo is reported to be fine and well marked.
Hope this helps some of you. I think that the coastal options are going to become more and more popular, especially as people find that all the road walking is killing their feet! Buen camino Laurie