You are eligible for visa free entry
Up to 90 days within any 180-day rolling period - and that count runs across the entire Schengen Area, not just Portugal. Days spent in Spain, Italy, France, or anywhere else in the zone all come off the same total.
Your passport should be valid for at least three months beyond the date you plan to leave Portugal. Carrying one with six months of validity is the smarter habit - most airlines enforce it, and border officers prefer it.
A valid Argentine passport with sufficient validity, as above, plus a couple of blank pages for entry formalities.
A return flight, a train to Madrid, or a bus crossing into Spain - anything with a confirmed date showing you plan to leave. A screenshot on your phone or a forwarded email is all you need; nobody is looking for a printed booklet.
Proof of Accommodation: Border officials may ask for evidence of where you will be staying, such as a hotel reservation, Airbnb confirmation, or host details.
A bank statement or a credit card with a working balance. The vast majority of Argentine travellers pass by without asking for this document, but having it somewhere you can pull up quickly costs nothing, and it answers any question in seconds.
Travel Health Insurance: Although not always requested from visa-exempt travellers, medical coverage of at least €30,000 is strongly recommended and may be requested by border authorities.
Check if you need a visa for your next destination
