This past week in Lisbon was hot.....really hot. The type of hot that makes you rethink your existence and feel bad for the thousands of years of human life before air conditioning.
The wonderful thing about Portugal is that a giant portion of the country is on the coast. Both of the country's major cities, Lisbon and Porto, have beach access.
Even after a summer of heating, the waters of the Atlantic Ocean that smash into Portugal's coast maintain a refreshing temperature. On a hot day (over 100 degrees F), the ocean doesn't feel like bathwater.
In Lisbon, the beach everyone goes to just outside of the city is Cascais, which is really fun to pronounce: cash-kai-sh-ka. Cascais is fun and beautiful, but it is crowded and the town is extremely touristy. Additionally, just getting tickets for the train to Cascais can be a several hour endeavor.
If fanny packs and tourists screaming in German is your thing, by all means, stay in Cascais. However, if you want to skip the tourists and the train, you are going to have to work a little harder for it. The reward is well worth it. THIS is where you really want to go to the beach.
I suggest renting a car from Lisbon and driving to Praia da Crismina or Praia Grande do Guincho (right next to each other), both of which are 15 mins (by car) outside of Cascais, and 40 mins from Lisbon.
Getting to Praia da Crimina or Praia Grande do Guincho without a car would be difficult. You would need to train into Cascais and either bike or hitchhike to the beaches... probably don't do that.
This area was one of the most beautiful stretches of coastline I have ever seen in my life. Huge waves crash repeatedly into the dark and rocky volcanic cliffs surrounding the beaches. Surfers battle the elements and ride into shore all day long. The beaches are speckled with colorful blankets and umbrellas.
The beaches were crowded, but the best news ever - VERY few tourists! Just locals coming to cool off.
The beaches are separated by a cliff with a hotel on top. The hotel, Fortaleza Do Guincho, coincidentally has a Michelin starred restuarant in it. If you are feeling extremely fancy, make a reservations in advance for lunch there during the day. It will be one of the best meals with a view you will ever have.
Both beaches are also 30 mins from the town of Sintra. You could also rent a car from Lisbon, spend a few nights in Sintra, and drive to the beaches from there.
Enjoy.... I hope you can make the trip out there. It really is a beautiful, beautiful spot.