Barcelona trip coming soon

Gents, I'm off to Barcelona. It's a business trip but I should have a few hours to kick around. I understand there are three or four major stations, and Sants seems to be the main one but a bit sterile, like Warsaw or New York Penn. Francia seems the most interesting, but I'm relatively uninformed. Anybody with experience? Thoughts on things to look for?

The first things that come to my mind.
Estación de Francia is surely the more interesting place for RENFE trains but personnel is not friendly with train enthusiasts.
The Tranvia Blau, that connects with the Tibidabo leisure park funicular, is operated by historic tramcars.
The narrow gauge lines that go to Martorell and over have, apart the electric passenger services, a good amount of diesel freight services that arrive to the harbour area.
Enjoy yourself.