- How to Get There from Barcelona: Andorra is a three-hour drive from Barcelona or a four hour bus journey (with Alsina Graells) Andorra might look closer to Girona than to Barcelona, but the roads from Girona to Andorra aren't great and it actually takes longer than going via Barcelona.
- What to See: Andorra is actually a separate country (the only country in the world where Catalan is the first language, although Spanish & French are widely spoken). Excellent for skiing and buying cheap electrical goods and jewelry due to the tax-free status of the country.
There are several points of interest outside of Andorra too. The mountain town of Vic, the stone-built village of Queralbs and of course all the lovely scenery.
To see all of this in day would be quite an effort if you were to organize it all yourself. Much easier to book a tour such as one of these:
Guided Tour of the Pyrenees
Three Countries in One Day - Spain, France and Andorra
This bus tour (with professional guide) takes you to all of the places mentioned above (apart from Andorra) and still gets you back to Barcelona in time for tapas.