Sesimbra lies in 'The Land of the Three Castles'. Sesimbra being one of them. Together with Setúbal and Palmela they make up the apex of the triangular isthmus south of the Tagus river.
Sesimbra can be easily reached from Lisbon via car: Cross the Ponte do 25 Abril, continue southwest to Setúbal and at the junction N378 head directly to Sesimbra.
By bus: Busses run regularly from the Praça de Espanha (Metro: Palhavã) and from Cacilhas. The trip takes about one hour and the last time I took it (September 2007), it was 3,60 EUR. For exact fares and schedule, go to Transportes sul do Tejo, or call +21.223-30-71. From the airport the easiest way to get to the Praça de Espanha is a taxi, which will run you 5,-EUR