We are thinking of a day trip to cascais by train from Lisbon. What can we do without a car? We enjoy walking, museums, good food
The centre of Cascais town is fairly compact and only a short walk from the railway station. It's a while since I have been there so I cannot be specific.
I live in Cascais without a car - so you can definitely fill a day trip.
When you get off the train, cross the round about and walk through the old town. You can ask directions to the bay of Cascais. From the bay, you can walk up past the old fort and the marina to a lovely walk along the sea. You can visit Boca do Inferno on this walk and finally make it to Casa da Guia. There are a number of restaurants overlooking the sea with lovely cliffs.
Alternatively, you can take the Buscas right outside the train station to Casa da Guia. The bus driver will tell you when to get off. After lunch, walk back to town, visit Boca do Inferno, etc.
If you visit on Wednesday or Saturday, the Mercado is fun to visit. Any local can give you directions.
Another thing is to walk from Cascais to Estoril. There is a great paradao (Walk way) along the bay.
and all but across the main road from the marina there's a lovely park called marechal carmona which makes for a pleasant way to spend a hour and from my last visit you'll find some of the wildlife aren't camera shy and don't mind getting up close to us humans.