San Sebastián
We were already living in San Sebastian, but its easy to get to by Madrid and most of northern Spain by train. We stayed in apartments, but there are countless reasonably priced airbnbs, hotels, and hostels. My favorite hostel is called "A Room in the City Hostel". Its direclty in downtown (called El Centro), has a lot of ameneties, and the whole city is walkable from here. From the hostel. you can walk directly to La Concha beach, San Sebastian's most famous crescent-shaped beach. There are floating docks with slides a short swim from the sand and you can rent cabanas, umbrellas, and more to enjoy the beach with. You can also rent paddle boards for the bay. Don't be alarmed that in Spain, sometimes people will go nude at the beach! You can spend hours here.
For sunset, take a ride up the old furniular to the top of Mt Igueldo on the left side of La Concha. At the top, there is actually an old amusement park that the Queen built in the mid 1900s. There is a cafe where you can sit and take in the gorgeous vista.
For dinner, theres endless tapas bars and restaurants to choose from. If you want something local, head to Parte Vieja and stop by in any of the tapas bars for traditional basque pintxos (basque for tapas). One of our favorites is simply called Barrio. For patatas bravas and fried calamari, La Mejillonera is extremely popular. For a nicer meal that is still reasonably priced, Atari, right off the steps of the old cathedral is amazing. Get the pulpo a la plancha if you are feeling adventurous!