Help on Sintra visit!!

There is a lot to see in Sintra. If you are going to go as a day trip then I would try to get there early, park and explore. I'm not even sure how many sites will be open late afternoon in October. We were there in April and my recollection is that they closed by late afternoon. I do agree that he crowds will potentially be less after around 4:00 but won't the sun be setting around 6:00?

We actually stayed 2 nights in Sintra, and if you could stay one night it would help with your concerns. We did enjoy the Quinta de Reguleira gardens a lot. Pena does have the stunning architecture outside. We also liked the National palace which was right in the heart of the town. I quite enjoyed it, but maybe just as it was less busy and a bit of a surprise. We hiked up to the moorish castle and Pena and walked a lot around the town.

You are correct in not wanting to drive into Sintra. But only being there in the late afternoon doesn’t give you time enough. You might be able to see one site but likely not more.

To me, the insides of both Pena and Reguleira are underwhelming. But the gardens and well at Reguleira and just the outside in total at Pena are pretty amazing. I really like both the gardens, exterior and interior of Montserrat. There is a small parking lot there and it’s a bit out of town. But, I don’t know how difficult it would be to drive there as I took an Uber.
You don’t mention if Lisbon is on your itinerary. If so, small group tours from Lisbon are plentiful and not that expensive. My first trip to Sintra was a small group and it was my favorite trip there.

I agree with kathrynj, the parks at Pena Palace and Quinta da Regaleira are quite amazing and it is easy to spend hours exploring. I would skip the palaces at both places. If I only had a little time and wanted to be "wowed" by just one park, I'd go to Regaleira since it seemed to pack more significant features into a smaller space. Monserrate also has a beautiful garden and the palace itself is lovely, with such intricate detail. I used Bolt to get there later in the day. There really weren't any other people around when I visited so I could take all the time (and pictures) I wanted. Fortunately when I was ready to leave, there was one Bolt driver sitting in the parking lot and he took me back to town. I think you're wise to avoid driving in Sintra if possible.

If I only had one day, I'd actually skip Cascais and just focus on Sintra. Not that Cascais isn't lovely (I'm spending several nights in Estoril in a few months), but Sintra is like no other place I've visited.

I enjoyed Nazare too and hope to return to spend more time there in the future as well. Have a wonderful trip!

Thank you all for the thoughtful and informative responses. We have decided to take a tour from Lisbon after our stay in Nazare.