Is it possible to travel from Rome back to Madrid without flying? I would like to do the Euro Select Pass (I believe that's what it's called) for 3 bordering countries - however Italy doesn't border Spain. My wish is to travel Madrid to Paris, then to Venice, then Rome, then back to Madrid via Barcelona and Madrid. Any suggestions?

Try this, by train:
1.- Take a day train from Rome to Milan
2.- Take the overnight Tren Hotel from Milan to Barcelona.
3.- From Barcelona to Madrid you can take a day train

For Barcelona-Madrid schedules: RENFE
For Milan to Barcelona:
Elipsos

Is not the pass you are refering to EURORAIL PASS?
It's for bordering countries, but not in the sense you mean: you can't "jump" from a country to another country which does not share border, but you can do "consecutive" countries. Your trip would be correct: Italy-border-France-border-Spain

Thank you!!

I have no first hand knowledge of this but I have read about them.

--- Ferries to Spain ------------------------------------------------------
Grandi Navi Veloci: (Call Center Phone: +39-010-582080)
From Genoa (Italy) to Barcelona ( Spain) - Departure every Mon/Wed/Fri - 18 hrs. trip

Grimaldi Ferries: (Call Center - Phone +39-010-582080)
From Salerno (Italy) to Valencia (Spain)

It's an alternative ...