Portugal is a great value for money travel destination. They've got history, sun, beach, sea, and wonderful prices. I allocated 6 days for my first visit to the country with Lisbon being my base. I usually wouldn't devote so much time to a smaller city, but was convinced I needed it to manage a few day trips. With a very affordable hostel at 30 euros a night for a private room in the city centre, it was still cheap to stay a little bit longer.
Lisbon has colourful maze-like hillside neighbourhoods and a reconstructed centre of wide, symmetrical streets and beautiful squares. The contrast is due to tragedy in November 1755 when a massive earthquake, tsunami, and subsequent fire devastated the city, killing an estimated 60,000 people.
My 5.5 days here ended up being quite packed, which validated my initial belief that a longer stay here was necessary.