Literally 'Saint Domingo of the Roadway', it was founded by a Saint and retired monk called Domingo [1019 to1110 AD] who created a settlement by the River Oja, which descends from the snow-covered slopes of the nearby Sierra de la Demanda to join the River Ebro at Haro. This is the river after which the Rioja wine region is named.
Santo Domingo is a key feature of the Pilgrim's Route to Santiago de Compostella and the settlement grew into a town with a Church, hospital and a bridge. Later in the 15th century becoming a city as it continued to flourish. A convent, a monastery and several mansions were built and this vibrant and prosperous environment continued to grow to the 6,000 inhabitants of today.
Santo Domingo is well worth visiting and if you seek a hotel you can do no better than the Parador in the 12th century former hospital for Pilgrims; it is luxurious with stately bedrooms and has an excellent restaurant. A visit to the Cathedral opposite is a must if only to witness the legend of the cockerel [there two in a cage there]; but also look at the splendid Reredos and other features. Then continue around the walled Old Quarter, including the Plaza de España, town hall and many attractive buildings, stopping for a coffee or something stronger at one of the many cafe bars.
Nearby are the Monasteries of San Millan de la Cogolla tucked away in the Sierra's foothills beneath the peaks of San Lorenzo. Gonzalo Berceo wrote the first text in Castillian Spanish in the 10th century at Suso [founded 550 AD] that looks down on the much larger Yuso that is a thousand years younger. Also in the foothills of the Sierra is Ezcarray that now serves the ski station above, but whose origins are based on the mercury mines in the vicinity.