Traveling by train
When you only have one day to visit a city like Santiago de Compostela, a tourist train is a good option - especially if you're travelling with small children. On our recent trip to Galicia, we went to Santiago but we wanted to go back to the hotel to sleep at night. So first we went to the Old Town and, of course, the cathedral. After being overwhelmed by so much beauty, we decided to catch the train, which leaves every hour from the Plaza del Obradoiro. It gave the kids a chance to rest, and meant that we could see more of the city. The tour is approximately one hour.
The guide explained everything - monuments, parks, churches, etc - quite succinctly.