Portugal is a full member of the European Union, and as such, E.U. citizens only need national identification cards to travel inside the country. Travellers hailing from Australia, Canada, New Zealand and the United States can enter the country and stay for a period of up to 90 days without a visa. Portugal is also a signatory of the Schengen Treaty, which means that once you’ve entered, you can travel to other Schengen Treaty states (most of Europe) within the same 90-day period.
If you’re not sure about your visa requirements in Portugal, check with your nearest Portuguese consulate or embassy for more information. Once you’ve arrived, it might be possible to extend your stay. Stop by a local SEF office to apply for an extension. Make sure you bring evidence of funds (like a bank statement) to prove that you can support yourself.