Lisbon, Porto, Barcalona and Madrid.

Just go to tripadvisor and look at "Top Things to Do" for each city. Chances you will find most of the same recommendations for "must see's" found in any forum, guidebook or travel website.

I have checked Trip Advisor for past trips. I found they are not always "accurate" with their descriptions. Some "top" locations and activities were very touristy. I was hoping to get truthful reviews ans suggestions from travelers who have been to these locations.

I don't know what an unbiased traveler is.

I agree that TripAdvisor is not ideal for sightseeing info. There are people whose reviews make no sense because they're so ill-informed they post them for the wrong sight.

Rick posts his top sightseeing suggestions for major cities on this very website. My tastes are not the same as his (I'm more into art and much less into pre-20th-century history), but I think he does a good job of highlighting a variety of sights that will generally appeal to most travelers. In all cases you'll need to click on At a Glance to see the list.

Porto sightseeing

Lisbon sightseeing

Barcelona sightseeing

Madrid sightseeing

While three nights may be sufficient for Porto, it's terribly short for the other three cities. It allows you only about 2-1/2 days to see a major city. I hope you'll be able to extend the trip.

Unfortunately, despite what the map suggests, ground transportation between Portugal and Spain is not good. Options are limited and infrequent--so much so that it is commonly suggested on this forum that people not try to combine the two countries on a short trip. You'll probably need to fly from Portugal to Spain or vice versa. Please be sure you buy multicity airline tickets rather than round trip so you don't have to fly back to the origin airport. Trains are fine between Lisbon and Porto and between Barcelona and Madrid.

If you absolutely don't want to fly, your best bet may be the Bla Bla Car Bus (yes, really) departing Lisbon at 9:45 AM and scheduled to arrive in Madrid at 6:15 PM. I have no idea how reliable that scheduled arrival time is. It's a long trip, and traffic could cause issues.

The quick pace and the asking for "must see's" I'm reading this as what I call a sampler trip, basically getting a taste of the two countries and seeing a bit in each location. Thinking about it that way, I'd like a bit more information before listing a bunch of sites that you can get by just googling. What do you like? Architecture, museums, looking out at beautiful views? How active are you? Any mobility issues? Do you like to see tons in a day, or just a few things, taking it easy.

So, off the top of my head a few places I enjoyed. Lisbon (Belem), walking along the Tagus River and seeing what you see which would include Jerónimos Monastery, Belem Tower, Couch Museum, perhaps grabbing some Pastel de Belém if the line is not too long.

Porto (Ribeira neighborhood). Walking along the river, listening to music and crossing the Dom Luís I Bridge to watch the sunset from Jardim do Morro (Gaia side).

The Rick Steves guidebooks are a good start for his curated view of the must see attractions in each of the locations.

We just returned from Lisbon and Porto. My husband and I are interested in culture, food, wine, with me having a much higher tolerance for art/history. We spent 6 days in Lisbon with a day trip to Sintra and day trip to Évora. We spend 4 days in Porto with a day trip to the Douro Valley.

Here are the highlights as well as things that were a bit of a disappointment.

Lisbon Favorites:

• Exploring the Alfama area and seeing a Fado show. The Alfama area is a place to get lost (it is easy to do even with Google maps). It is a place to see some fantastic street art, little boutiques, and small eateries. We took a tour with Eating Europe that included a Tuk Tuk tour along with a food tour. Afterwards, we went on our own to explore.
• Visiting a miradouro (a scenic outlook). There are miradouro’s throughout Lisbon, I frequently visited the Miradouro de Sao Pedro de Alcantara which was near our hotel in the Barrio Alto and is close to the Rossio Train Station. This one has a nice cafe where you can order my new favorite drink (the Port tonic) or bring you own and watch the sun set.
• Belem, especially the Jermonio’s Monastery. From there you can go see the Monument of the Explorers and the Belem Tower. The best Pateis de Nada was at the original Pasteis de Belem.
• Carmo Convent: this was such a nice surprise to visit, it has a great square in front of the convent, and access to the Justa Elevator from the top.

Lisbon Disappointments:

• Sintra: this was a miserable experience, pouring rain and wind. It might be better in on a sunnier days, but in the rain with wind, we wished we would have skipped it. It was so foggy, we could barely see the castle from a distance.
• Baixa area: while the river was nice, the rest of the area was too crowded for us. After visiting, I was glad we stayed in the Chiado/Barrio Alto area.

Porto Favorites:

• Free walking tour with Sandeman’s tour. Our guide was amazing and we learned so much about the history of Porto. It was a great way to introduce us to the city and helped us determine which sights we wanted to visit.
• Eating Europe Port Tour: This was one of the best experiences we had on our trip. They not only took us to Vila Nova de Gaia for port tasting, we had the privilege of touring one of the older port houses in Portugal, owned and operated by a Portuguese family. We ate at neighbor places, including a grocery store. We spent our lunch talking with the owner, who taught himself English and was happy to help teach us some Portuguese. The food was rustic, filling, and the local merchants were delightful.
• Day trip to the Douro Valley. We love wine and food and this trip was amazing. It included a boat trip, drive through the valley, two tours/tasting and a lunch at a small, local winery.

Porto Disappointments:

• Vila Nova de Gaia on the river. It was crowded and while it had a great view of Porto, it was not to our tastes.
• Not giving Porto enough time, we really like this city and wished we had allotted another couple of days.

A couple of notes

• Both Lisbon and Porto are hilly and very slippery in the rain. Wear shoes with really good traction if you are going in October as this is a bit more of the rainy season.
• We started out using public transport, but Uber and Bolt are so inexpensive, we switched for the convenience.

Hope this helps. Without knowing your interests, I can only share our perspective.

Lucky for us, we share the same exact interests. Your response was exactly what I was looking for. Favorites and disappointments clearly stated. It will be a great help in planning our trip. Thank you very, very much. Hopefully we can get the same type of response concerning Barcelona and Madrid or possibly any other part of Spain close to those cities.

Perfect timing for us! We are ending a Viking cruise in Barcelona next Oct and was thinking of Lisbon & Porto too. Following for all your great tips since this will be a first trip to Europe for us!

The favorite part of Lisbon for us was Belem. Do not miss the Jeronimos Monastery, beautiful Manueline architecture.