Humberto Delgado airport is on Lisbon’s northern outskirts, 7 km from the center. There are regular flights from the main airports throughout Europe, as well as from the USA. A taxi to the center costs €15-18. Aerobus Line 2 runs to the riverfront at Cais do Sodre, via the central Avenida de Liberdade, Rossio and Praca Comercio, every 20 minutes and costs around €4.