For what it is worth, Decathlon does regularly carry Salomon and Merrill brands for hiking boots and shoes, plus their house brand Quechua. They also carry Adidas, Nike and other world class brands of training and running shoes. I frequently shop in Decathlon stores while in Europe, and particularly in Spain. They offer good value for money. I wish we had them in the US.
But, fitting footwear is a serious and highly individualistic thing. So, think carefully, and consider adding another thin layer of liner socks, or panty hose material "footies," on a not-yet fully-broken-in pair of new shoes, especially if they are of a brand you do not normally use. This added "slip layer" will help avoid blisters.
I have been to the Ponferrada Decathlon store and can recommend it. It is on the west side of the city, across the river, in the "new" section. You can access it on foot from the ancient center. I recall it was about a 20-minute walk from the castle.
From the Decathlon store to the point where the Camino exits Ponferrada, back on the east side of the river, was about another 20-30 minute walk...all through the city. The trip is in a "half circle" from the castle to the store to the Camino exiting from Ponferrada. You walk in a clockwise direction.
Laurie "Peregrina2000" is likely correct about buying shoes at Decathlon, but IMHO only for their house brand. They typically offer very good value for money across their entire product lines. However, if you needed to buy shoes or boots to wear on the Camino, like right out of the store, their house brand likely requires more of a break-in period. See the "slip layer" tip above...
I have also been to the El Corte Ingles store in Leon. I bought some Camino stuff there in 2014. Like most El Corte Ingles stores in larger cities...it is HUGE! Try not to get disoriented.
Look for the "deportes" (sporting goods) department, usually on the first (0) or second (1) floor. As I recall, the store is located downtown, but on the east side of the main drag...it is maybe a 15-minute in-city stroll from the center of town. The streets are all well marked.
Their prices are not inexpensive, but they DO offer world-class products and brands. Their house label is called "Boomerang." At Santiago, in July, I obtained two very nice microfiber polo shirts for only €11 each. Yes, they were on sale, but I wear like a size 56 (XXL). My clothes are all larger than usual, even in Spain where sizing runs small. I consider this a steal! But, I hit the end of season sales that run in July and August each year...
So, do follow the advice given here. All of it is well-intentioned and informed by experience. However, do not shy away from Decathlon if you are near one. This is especially true if you happen to wear either Salomon or Merrill hiking footwear.
Just a related point, Decathlon stores are usually all located on the outskirts of town as they are very large and on one level. Plan on taking a bus or a taxi to get to one. In Ponferrada, the Decathlon store is more "in town" but is still on the western outskirts of Ponferrada and is not as large as some others. There is always plenty to see and temp the wallet...
For example, the one in Santiago is at the very end of the number C5 or C6 bus line in Costa Vella. The store is literally across the street from the bus stop. The bus ride from Plaza de Galicia is about one-hour, but costs one-euro. A taxi will cost about €8 from Plaza de Galicia, but takes 10 minutes. Usually, I take a taxi there, then plan my shopping to coincide with the bus schedule to return.
I hope this helps.
