Here my personal tips for some special local activities:

... a gentle trip with the tram to the beach: After renovation work, the historical Sintra Tram has come back to the beach, resuming its original route between Vila de Sintra and Praia das Maçãs, thereby connecting the Mountain to the Sea. The train stop is located 2 minutes from Casa José Ricardo; trips are frequent during summer (from mid June), at other times of the year our tram operates on weekends only.

... a guided botanical walk in the Sintra mountains with renowned Portuguese specialist in the field of medicinal and aromatic herbs and book author Fernanda Botelho. Fernanda studied medicinal plants at the Scottish School of Herbal Medicine in London, where she worked several years, acquiring her knowledge in organic and sustainable farming. Back in Portugal, she develops and organises trainings and workshops about medicinal herbs and has installed gardens of medicinal plants in the parks and gardens of Sintra, including Monserrate, Parque da Pena and Capuchos and writes books. Combining a walk with Fernanda in these beautiful gardens with learning about the medicinal properties of the local plants is a rich and stimulating experience!

... Wellbeing, Spa rituals and beauty treatments. Spoil yourself in the luxury environment of several luxury spas nearby which offer a wide range of holistic wellness, rejuvenation and beauty treatments, administered under the guidance of expert therapists.

Also nearby...
Enjoy a stunning view of Guincho beach while relaxing with a drink in the lush atmosphere of Moinho Dom Quixote, a bar and restaurant located in a restored windmill on a hilltop near Cabo da Roca (remember to take some cash with you, as they don't accept card payment);
.. . explore the freemason's rebirthing tower at mysterious Quinta da Regaleira;
... swim or surf at nearby beaches - Guincho, Praia das Maçãs, Praia Grande, Adraga, Ursa, Ericeira.

Spend a 'day out' in Cascais: Combine visits to the Paula Rego museum and the Farol Santa Marta museum (both very stylish) with some time at Cascais beach. If you like to shop for gifts, look for a sweet place called the 'House of Wonders' which is also a cafe and is near the Misericordia church. It has a lovely roof terrace and delicious cakes and salads - perfect for chilling out after the beach. There is now a craft and food market at the Mercado Municipal in Cascais on Sunday - small but well worth a visit. For local souvenirs, the covered stalls at Boca do Inferno (on the seafront, from Cascais in the direction of Guincho beach), where you can buy various local handmade crafts, incuding ceramic plates and knitted ponchos at very reasonable prices. And for clothes shopping, pop into Casa da Guia.

A bit further away... Dolphin watching in the Sado estuary: Tour operator Vertigem Azul is offering tourists the chance of a close-up view of the rare bottlenose dolphins in the Sado estuary, south of Lisbon. Guided boat tours along the picturesque Arrábida coast and into the estuary operate throughout the year, with snorkeling stopovers included during the summer months.