In Spain, that's difficult. Spanish railways (RENFE) are so customer-friendly that they don't share their complete timetables with the rest of the world and want a reservation for most trains other than suburban trains. They even have regional expresses with mandatory reservations…

Some of the suburban trains (Cercanías, or Rodalies around Barcelona) can get you quite far though.

And there's the odd regional train that doesn't require a reservation. In 2015, I used one from Madrid to Segovia and I see it still exists. Although a single fare for this would just be €8.55, so even a return is still quite cheap.

The in fact ONLY region where this is feasible is Catalunya-there they have also Regional-express on major lines, mostly along coast. BUT; then a pass is more expensive as buying normal tickets! F.e. I was myself in Barcelona last week and did a daytrip to Tarragona (old roman centre+fort)-ticket was about 5€ for 90 KMs., with senior discount. In a region around Barca is also a dense rodalies=local suburban around, with even daytickets etc . But again except some old-style seaside resorts not really serving many touristy places. Such cercanias systems exist around all main cities and offer very low normal prices. The best known/used is from Malaga west via Torremolinos to Fuengirola-said to be the one that brings in most money.

In Andalucia=far south, malaga/sevilla/cordoba are some MD=Media Distancia trenes besides the expensive AVE=hispeed. But you have to reserve them all-add. cost 6€ on pass.

Spain is a big empty desert with some large cities spread out in the middle. The Espanoles themselves go to the north coast in summer-they want cooler weather, as they have heat enough. there is a narrow gauge line all along that coast, still using former name FEVE-but also with just 1 or 2 daily trains on long distance. Not really feasible for daytrips!

NOTE: as all cerc. stops are also gated, even there using a pass is sometimes a PITA: you have to go to counter, show pass, and then they can ´untie´ a gate for you. If there is no one=bad luck, buy ticket! This is because they have switched over to chipcard entry, except for now around Barca.