The Lisbon Portela Airport is the main international gateway into Portugal. TAP is the national Portuguese airline, though several low-cost airlines (including Easyjet and Vueling) also fly into the city. Renting a car can be pricey if you are traveling alone: gas is expensive, many highways have tolls, and parking in the city is difficult. Do not fret, however, as a subway line and a network of buses, taxis, and shuttles connect the airport to downtown.
Within Lisbon, the transportation options include buses, subways, taxis, trains, and the classic yellow trams. The easiest move is to put money on a green card (Viva Viagem) and use this for every form of transportation. Trains take you to beaches and villas, including Sintra and Cascais. Ferries enable you to cross the river and see Lisbon from the other side. Be sure to check out the famous municipal elevators like Lavra or Santa Justa: historic lift systems that make this city's steep hills more navigable.