There are two main road routes from Lisbon, Portugal to Cascais, Portugal.
The A5 Motorway cuts through an urbanised/industrialised area that used to be forest. It is not very scenic although it is quicker. Tolls apply. One can see the mountains of Sintra in the distance.
The "Marginal" N6 is a lovely drive along the Tejo Estuary WHEN there is little traffic. However, it is a major busy urban artery and unfortunately, one needs to concentrate on driving rather than taking in the sights. There are no tolls on this route.
By Alquiler de Coches from España (Avenida Marginal de Cascais, Estoril) [CC BY 2.0], via Wikimedia Commons