Across much of Europe, but especially in Spain and Portugal, 'Semana Santa' or Holy Week is a time of many local festivals, religious observances, public processions, and general holiday making. Also, in many European countries, including Spain and Portugal, people have off from work on Holy Thursday and Good Friday, leading into Easter Sunday. They then have and Easter Monday off as well.
Many Europeans will combine these 'free' days off with several "bridge days" to have a week to ten days to walk a Camino, with minimal charge to personal time off. During the week before and week immediately after Easter, there is a surge in traffic along the Camino routes.
This surge is most pronounced on the
Camino Frances, and Camino Portuguese from Porto north. While the surge is evinced all along these popular routes during that time and accommodations become difficult at most all large towns and cities for this two-week period, it is most pronounced on the final 118 km from Sarria to Santiago.
Practically speaking, what this means for any pilgrim doing a longer walk and being there at this time of year, is that advance reservations for accommodations are near mandatory. You will see more folks walking on the trails, eating at cafes, etc. For this brief, two-week time, the surge in traffic approximates summer volumes. So, be prepared...book ahead...
Also, and for what it is worth, Semana Santa marks the 'informal' start to that year's Camino season. From Semana Santa and Easter, the Pilgrim Office goes into summer hours, more albergues are open, and the number of pilgrims starts to increase seasonally. FYI, this coming year (2019) Easter falls on Sunday, April 21.
Immediately after the two week period bracketing Easter, traffic falls off again, but not to winter levels. For example, I intentionally time the start of my Camino each year to be shortly after this window, or during the last 10 days or so of April. This avoids much of the Easter "blip" or spike in traffic. So, for 2019, I would plan to start around Sunday 28 April, 'mas or menas...'
What comes immediately after this, though is the annual "student wave." This is when university students are on escorted group trips on the Camino as part of a course. This phenomenon runs from the last half of April through the end of May.
At around the same time, there is a seasonal wave (pig in a python) of commercial travel agency organized groups. Most of these "tourigrinos" are also experiencing a 'taste of the Camino' and do mostly the Sarria to Santiago segment. These folks also stay in commercial lodging, not municipal or parochial albergues.
Together, these groups typically soak up commercial lodging along the
Camino Frances especially from Sarria to Santiago. So, again, book early.
If Booking.com says they are full, contact the property directly, using e-mail to try to make a direct reservation. All properties hold back rooms.
In a pinch, ask the proprietor where you are staying today, call up-the-road to make a verbal reservation for you at your next planned stop. The innkeepers all take care of one another. This usually works, provided you can communicate your request effectively.
I suggest using either the Google or Microsoft translation apps to pose the question. Save the canned request to your smartphone and change it to suit the day and location. This works great for me.
Once you make any reservation, SHOW UP! If you cannot show up for any reason, PLEASE notify the property by e-mail, so another pilgrim can have your no longer needed bed or room.
Hope this helps.