In addition to the beaches listed here, you can be adventurous and take the Cascais train line from Lisbon's Cais do Sodre station. Each stop from Paco de Arcos until the end of the line, Cascais, there is a beach. It only takes 20 minutes to get to Paco de Arcos by train.
1. Costa da Caparica Beach
How far from Lisbon: About 20km (12 miles)
How to get there by public transport: Bus to Caparica (departs from Praça de Espanha bus station), then a 5 minute walk to the beach.
How to get there by car: Take the IC20 road. The journey takes about 30 minutes.
2. Guincho Beach
How far from Lisbon: 35km (20 miles)
How long: 40 minutes (by car).
How to get there by public transport: Take the train from Lisbon to Cascais and then take the bus from Cascais to Guincho. The bus journey is about 20 minutes.
By car: Take the A5.
By bike: You can get a bike in Cascais and cycle on the path to the beach.
3. Adraga Beach
How far from Lisbon: 45km (30 miles) from Lisbon
How long: 50 minutes(by car) from Lisbon
How to get there by public transport: You'll want to get to Sintra first, which is easily accessable by train. See here for more on how to get from Lisbon to Sintra. From there, you can take a taxi from Sintra to the beach (around 15 euros) or you can take a bus to Almocegeme. From Almocegeme, it is a 20-minute walk.
By car: The journey takes about 50 minutes using the A5 to Adraga from Lisbon. Slightly longer if going via Sintra using the A16. Both are toll roads.
4. Meco Beach
How far from Lisbon: 40km (25 miles) south of Lisbon
How long: under and hour by car
How to get there: Public transit requires a transfer. From Praca da Espanha bus station in Lisbon, take the bus to Sesimbra . From there, you can catch a bus to Meco beach.
By car: Take the EN377/N377.