Seen a few posts about these topics so thought I'd share my recent experiences.
Trains, the Renfe local and regional medium distance trains all take cycles at no extra charge. All trains will have doors with a cycle logo, these doors are your preferred entrance point. The carriage floor here (on most trains) will be lower and you will be able to wheel your bike directly into the carriage as the doors open to platform level. You'll find good space to stand sit and tether your bike, here's mine.
I say preferred because there is one problem, if you the train is late, or it's a particulary long train you may only have seconds to find the designated bike door, once the warning beeps start, forget it, the doors will shut in 2/3 seconds, I know this. The good news is that the space within every door entrance is large enough to accomodate 2 bikes without too much hassle, you may have to move them around as people come and go but unless it's rush hour in, say, Barcelona you'll be fine. Nobody cares, neither passengers or employees that you have not used the "cycle" access points, don't worrry.
I am a non-helmet wearer, I've cycled Andalucia and Asturias within the past 3 years and was blissfully ignorant of the fact that in certain circumstance helmet wearing is obligatory until I saw a post on here. On those 2 trips I often asked policemen for directions, including the Guardia Civil who's job it is to enforce that law. Not once was I asked to wear or produce a helmet. This year was different, I was cycling in Catalonia and was told that the law was enforced there. Still, I decided not to wear one or buy one to hang on the rack. This time I went out of my way to ask police for directions. Same result, from Girona to Tarragona via Barcelona not once was the lack of a helmet mentioned.
Trains, the Renfe local and regional medium distance trains all take cycles at no extra charge. All trains will have doors with a cycle logo, these doors are your preferred entrance point. The carriage floor here (on most trains) will be lower and you will be able to wheel your bike directly into the carriage as the doors open to platform level. You'll find good space to stand sit and tether your bike, here's mine.

I say preferred because there is one problem, if you the train is late, or it's a particulary long train you may only have seconds to find the designated bike door, once the warning beeps start, forget it, the doors will shut in 2/3 seconds, I know this. The good news is that the space within every door entrance is large enough to accomodate 2 bikes without too much hassle, you may have to move them around as people come and go but unless it's rush hour in, say, Barcelona you'll be fine. Nobody cares, neither passengers or employees that you have not used the "cycle" access points, don't worrry.
I am a non-helmet wearer, I've cycled Andalucia and Asturias within the past 3 years and was blissfully ignorant of the fact that in certain circumstance helmet wearing is obligatory until I saw a post on here. On those 2 trips I often asked policemen for directions, including the Guardia Civil who's job it is to enforce that law. Not once was I asked to wear or produce a helmet. This year was different, I was cycling in Catalonia and was told that the law was enforced there. Still, I decided not to wear one or buy one to hang on the rack. This time I went out of my way to ask police for directions. Same result, from Girona to Tarragona via Barcelona not once was the lack of a helmet mentioned.