2-day itinerary for Sintra, as suggested by ChatGPT

Sintra is lovely and I'm sure you'll have a great time. As a general disclaimer, I'll say that I tend not to trust AI for many things- remember it's not querying a database of e.g. train times, it's a probability machine that is just predicting what is mostly like to come next based on its training data.

Of the sites you've listed I've only been to Pena Palace. I don't remember much in the grounds, the main part I remember is inside the house itself. If you're planning to spend an hour and 40 mins there you can definitely visit the inside, which to me is worth it. I also notice this itinerary only gives you 40 mins for lunch, which for me would be very short especially if I'm on holiday. I will leave it to others to comment on the rest. Good luck with your planning!

The itinerary is quite good at a nice easy pace.
My only suggestion is that you might consider overnighting in Sintra, once the day tourists leave it's a lot less busy and more relaxed.

I've stayed in Sintra and hiked up and back to Pena Palace and Moorish Castle. I don't think its so steep that you have to worry about your knees unless that's already an issue for you, and you'll be on an established trail. I took a Bolt out to Monserrate and back, but I'll admit now I'm wondering if I should find out more about the walking trail you mentioned for next time I visit.

I agree with the suggestion of spending a night if you can make it work.

We visited Pena and the Moorish Castle last Fall, the walk between the two is easy. We took a dirt trail through the trees with a slight incline up to Pena. It was easy. I think you should double your time at the Moorish Castle. It's about a 15 minute walk along the trail from the ticket office to the ruins, and if you want to walk the walls you could use an hour. I'm not sure how long the walk back into town is. We used Bolt instead of the bus or walking.

Thanks to all for the input. We did consider overnighting in Sintra but decided against it -- the cost of renting an Airbnb for 5 nights vs splitting up over 2 different stays (both financially as well as the time and effort of packing and unpacking and storing luggages between stays) is just too much.

We will probably take more time at each location than what ChatGPT suggested, and I see there is even an outfit offering free walking tour in Sintra, so we will probably end up spending more hours each day in Sintra. I was more interested in getting the validation on its estimated walking time between locations, and it sounds like you folks are in agreement with ChatGPT's estimates, so that's reassuring.

Your itinerary is very doable. We had a similar 2-day visit to sintra back in March but with a few tweaks. We stayed in sintra overnight. And we visited Cabo da roca and azenhas do mar in addition to the sites you planned. In the afternoon of day 2 we took a bolt to Cascais, had some seafood and spent an afternoon there before heading back to Lisbon by train.

I do suggest that you consider taking taxi or bolt straight to Pena palace instead of train. Less stress and not that more expensive. Then, for your downhill walk after moorish castle, instead of walking the paved road, find vila Sassetti on google maps. It’s part of a scenic trail that leads to old town. The starting point of that trail is a parking lot just a few minutes downhill from moorish castle entrance. Pena+moorish+hike back for lunch is exactly how I planned our first morning but had to take a taxi instead as the kids were tired and hungry. But lots of people say the hike was one of the highlights for them.

Pena, moorish, Regaleira, Monserrate, all fantastic. Cabo da roca was underwhelming and if I ever visit sintra again I’d skip.