There are bridges across the Rio Tejo, but ferries are a quicker and much nicer option when you're headed to neighborhoods south of the city. Besides avoiding the traffic, you get amazing views of the Lisbon skyline. Ferries to nearby communities of Almada and Cacilhas are run by Transtejo Soflusa from terminals at Belém, Cais do Sodré, and Terreiro do Paço.
Transtejo Soflusa. 210 422 400; www.transtejo.pt.