Portugal, which shares the Iberian Peninsula with Spain, is a beautiful country full of historical and natural wonders. I have friends who spent their entire vacation in Portugal this year and strongly recommended it. We had one day to explore the capital city of Lisbon while on a cruise.
Lisbon is a large city, 100 kilometers square with a core population of 545,000 people which grows to 2.8 million if you include the surrounding area. The main part of the city was rebuilt after a devastating earthquake and tsunami hit in 1775, making it feel modern. From the cruise port it is a short walk to the main square that faces the waterfront from where you can explore the old city centre.
Since we wanted to see as much of the city as we could we took the Hop On / Hop Off bus. The red line, which covers the old town loop, 
takes about 2 hours and stops at the cruise port. The city centre is divided into a number of neighbourhoods, each offering different things to see and do. If time permits pick an area and walk around at your own pace to really discover the city.
Belem has some of the best sightseeing, including the Monastery of Jeronimos, the Museum of Ancient Art and the Monument to the Discoveries, an impressive tribute to the explorers who brought Portugal power and riches long ago. Belem is the last stop on the outward portion of the red line loop.
Alfama, closer to the city centre, feels more medieval and should include a visit to Castelo de Sao Jorge to take in some amazing views of the 
city. If the upward climb is a concern there are funiculars that will take you up to the castle. Bairro Alto and Baixa cluster near the waterfront and offer great shopping and restaurants, as well as access to a number of public beaches.
We hopped off near the main square of Praca do Comerico to take pictures. Walking through the arch located at the back of the square takes you to the main pedestrian street, Rua Augusta. We found a little café off the main drag, nicely shaded, for lunch. Since Lisbon is a port town we knew that the only thing to eat would be seafood. A shared calamari and two plates of freshly grilled cod washed down with a local brew was both delicious and economical. We finished the meal off with a custard tart, those tender, flaky, creamy pastries that personify Portugal.
We were there in late May and the most lingering impression I have of the city if the smell of jacaranda trees in violet bloom. There were a few streets we traveled down in our open air bus that surrounded us with such a pleasant aroma I could only inhale deeply and wish it would never end. Smells can trigger some of the best memories and I am so sorry that I could not find a way to share that with you.
The other memory I have is of the heat. It was a beautiful day that registered 35°C with a brilliant blinding sun. Those of us sitting at the top of the bus stayed in our unprotected location despite the burning rays so as not to miss a minute of what Lisbon had to offer. I found a small container of sunscreen in my backpack that I shared with my fellow travelers until we had squeezed it dry, a simple gesture that bound us together in our shared travel experience.