The regions surrounding Lisbon have something for everyone. Whether you are looking for perfect sandy beaches, impressive monuments, or historic castles and towns all can be reached from Lisbon.
Sintra is widely regarded as the best day trip from Lisbon - most, including myself, would suggest giving yourself two full days in the region. Sintra is 25 km west of Lisbon. It has a cooler climate and was a favorite of Portuguese royalty.
Sintras has a plethora of things to see. Its sights include the National Palace, the Moors Castle, Pena Palace, Quinta da Regaleira, Seteais Palace and Monserrate Palace.
Sintra can be very busy so expect crowds, especially in the summer months.
Here is a full guide to Sintra.
How to get there: Book a day trip from one of the many agencies (they run about $20-30) and enjoy being chauffeured around the massive area or take the train to Sintra and then the 434 tourist bus around the major sites.
A very short train ride from Lisbon, Cascaus is a historic fishing port full of beauty and tranquility. It is still a town for the rich and famous with many mansions lining its roads. It offers a beautiful beach, Parque do Marechal Carmona - a beautiful serene park, a free museum - Museu do Mar-Rei D. Carlos and historic monuments.
Three kilmoeters west of Cascais is Boca Do Inferno also known as the mouth of hell. It is a cliff side where the seawater beats into the side and sounds like a huge cannon being fired.
Palácio Nacional de Queluz
This beautiful palace is only 14 km North of Lisbon and is easily accessible. It was built between 1747 and 1794 for King Pedro and his wife. The gardens are massive and stunning and the inside is reminiscent of Versailles. If you love palaces this is a fantastic day trip.
How to get there: take the Sintra line train from Rossio to Queluz-Belas station. A 15-minute walk following the signs will lead you to the palace and gardens.
Cabo da roca
A stunning cliff side that is the westernmost point in Europe. It has amazing views and a gorgeous lighthouse.
How to get there: only accessible by car, worth the rental!
This small town holds one of Portugal's most impressive monuments: the Mosteiro Pálacio Nacional. The Baroque palace is from the early 18th century and is stunning in person. It was planned to be a simple monastery but was quickly upgraded to include a palace and basilica.
How to get there: there is spontaneous bus service that connects Lisbon and Sintra with Mafra but I wouldn't trust it. Rent a car instead.
Items I used on my day trips
I cannot recommend the pocket lonely planet guides enough. They are so small and hold so much information, you can easily throw it in your back pocket or bag!