Cascais is a great day trip from Lisbon. There are trains running between the city and the small coastal town regularly. This former fishing village is now an upscale vacation destination with pretty beaches, cute cafes, and lots of shopping. Be sure to walk the coastal promenade between Cascais and the next town over, Estoril.
A short train ride along the shore from Lisbon's Cais do Sodré station leads to Cascais, a formerly quaint fishing village that became (along with neighboring Estoril) a popular resort favored by European nobility and kings in the early 20th century. Today it is a colorful cosmopolitan town with elegant pedestrian streets, luxuriant villas, fashionable shops, restaurants and bars. Gayle and I actually arrived here on a bus from Sintra and took the train back. We had fun walking along the water, window shopping, and having Dinner at Restaurante B&B before we returned to Lisbon.
I loved Cascais. I decided on getting our hotel in Cascais over Lisbon because I wanted to be in a quiet(er) area near the ocean. I learned of Cascais over the internet and I'm so glad I stayed there. The town is small but really nice. There are areas with upscale stores but we more or less enjoyed walking around the restaurant/cafe side of town. We ate some phenomenal seafood, chicken piri piri and had great coffee.
... you can easily reach by train this lovely town too. Once a fishing village, Cascais is today a popular seaside venue.