Take in consideration when you plan a rest day on the Camino that you can stay only one night in most of the albergues. It’s reasonable to take rest days in locations where you can check into a hostel, or hotel. The hostels and pensions will cost you about 20-25 Euros per night and the hotels are 30-40 euros for one person.
There are lot of interesting and nice medium sized cities all along the Camino like Estella, Santo Domingo de la Calzada, Astorga, Villafranca del Bierzo and Ponferrada but the larger ones like Pamplona, Logroño, Burgos, León have plenty to do during the day and also in the evening. There are so many attractions in these larger towns especially during the weekends that you can easily spend here more than one day to rest.