I relied on this forum for my research before the trip, so I thought it would be nice to share the practical tips learned from the trip, for the benefit of future travelers.
Walking in Lisbon is not as bad as people made it to be. My wife and I are in our early 50s. We are healthy but not super athelets by any means. Our Airbnb is near the Intendente metro station in the Mouraria neighborhood. We took several free walking tours during the 5 days. Meeting places for the tours were at Praca Camoes and Praca Comercio (main plaza downtown). We walked from the Airbnb to those plazas (25 minutes or so), then walked 2 hours on the tour, then walked back home. Yes, we were tired when we got home, but it's a good kind of tired, without any physical stress, and never felt that "it's too much". So, unless you are obese or have mobility issues, you should be able to explore a lot of Lisbon on foot. It's more fun to do people-watch and sightseeing while walking than going point to point directly to the destination, as we sometimes discover things or run into pleasant surprises during the walking journey.
Bolt is great. When waiting for luggage at Lisbon airport, I noticed a billboard advertising Bolt service with a promotion of 70% discount for the first ride with a code “visitlisbon”. We only used Bolt twice, as we walked most of the time, took Metro/Bus sometimes.
We made the mistake of taking Metro to our AirBnb. The exit from the underground Metro station (Intendente) to street level was by stairs only – no elevator or escalator. Had to carry our heavy suitcase up the stairs – fortunately a passing young man offered to help. The walk to the Airbnb was only about ½ mile, but it was tough dragging a suitcase through the narrow cobblestone sidewalks. So, despite my earlier recommendation of walking whenever you can, don't try to do that with suitcases.
We bought Navegante cards for zapping. It worked out great. However, there is one quirk not well known by tourists: while the Navegante card can be used on metro and bus and tram, if you change the mode of transportation, you will get charged for each separate ride, i.e. no free transfer. But if you stick to the same mode, you only get charged once. (You still have to tap the card on the second or third ride, but it won't get charged.) When we went to Belem from Intendente, Google Map tells us to take Metro then switch to a bus, but it would have cost 1.66x2 euros. Instead, we took 2 buses. It ended up being 10 minutes longer, but it cost only one zap, and it's more fun to looking out of the windows of a bus then being in a Metro underground.
Sintra is wonderful. Most of the attractions can be booked online -- if you buy tickets at least 3 days in advance, there is a 15% discount.
(1) The first day, we booked a walking tour at 11 as a way to get an overview of Sintra, so we took our time in the morning and walked to Rossio station then took the train to Sintra. The tour spent some time in downtown Sintra and around Sintra Palace (the free portion of the grounds), and ended at Jardins do Palacio de Seteais, where you could get a view of Pena Palace far away. After the tour, we kept walking another 45 minutes and reached Quintinha de Monserrate. It’s not as famous as the other 4 main attractions in Sintra partly because it's farther away, but we really enjoyed walking around inside the building as well as the grounds. We were there for 3 hours, but could have spent all day just at this one place.
(2) The second day, we wanted to cover 3 attractions, so we took a Bolt from our Airbnb directly to the entrance of Pena Palace. With the discount code, we paid under 20 euros for the ride vs 17 euros for 2 people if we took the Metro then train then 424 bus, and we saved at least 1 hour.
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