6 days only! In to Madrid and out of Barcelona

My two favorite places "small places" in Spain were Montserrat (day trip from Barcelona) and Segovia (outside of Madrid). We traveled by high speed train between Barcelona and Madrid (buying our tickets early at a substantial discount) and found it easy and restful. For us easier and cheaper than flying and when you include traveling to and from the airport --faster.

It is only 2.5 hours from Madrid to Barcelona via train It would easily take that much time to fly or more with the travel time to airport and amount of time you have to arrive at airport before flight.
Train you do not have to check in that early before you leave. Do not have to worry about what you are carrying on for luggage as you get on and stow your luggage yourself on the train.

Train arrives quite centrally in Barcelona with easy access to local transportation

To get out and see some countryside and mountains. From Barcelona, it is a 1 hour train ride from Placa Espanya to Montserratt a monastery build into the mountain that is accessed via cable car or cog train. I would recommend the cable car ride. The views are wonderful even on a foggy day. Buy your tickets at the Placa Espanya Station R5 track Decide ahead of time as your ticket includes 1 hour train ride and the cable car or the cog train. Make sure you buy a round trip ticket.

The train ride Madrid to Barcelona is fast but not at all scenic. You will not see anything remarkable.

Your options for going somewhere else depend on what you have planned to do during your stay in Madrid and Barcelona. There is no way to say definitely if you have time to go somewhere else because you do not say in this posting what you have already planned that you do not want to miss in the 2 cities.

Someone mention Montesarratt near Barcelona but you may be able to go to El Escorial and Segovia on a day trip from Madrid https://el-escorial.com/

It would also be useful to know the date of the trip.

I'd probably want to have a couple of options for side-trips planned in case of a weather problem. Some places are OKish in the rain; others not so much.

It would be crazy to fly now that they have fast trains between Madrid and Barcelona. Flying is so much more of a hassle and prone to delays, trains go city center to city center. Six days is not much, on my next trip to Spain I would like to spend five nights in Madrid alone not counting day trips. But I love Madrid, and most people could probably deal with two full days. The problem is there are many great day trips of Madrid. Segovia, Toledo, El Escorial. Monserrat out of Barcelona is a good one, too. For me Spain is about the cities, have never found the countryside to be scenic. But I have not seen the whole country. The closest thing to scenic countryside might be Montserrat area. Those two cities will keep you very busy but it's your trip so if you want to venture out go for it.

I agree that much of the countryside immediately around Madrid isn't very scenic. But what you see at the end of the trip (Toledo! Segovia! Cuenca!) makes up for it.

You each got my heart pumping and excited! When I booked this travel, I had no idea Spain was such a vast country with each piece having its own personality. We are going very soon, the end of April, arriving on Sunday in Madrid, very early AM, and leaving on Saturday, from Barcelona. The only plan we have is a museum on Friday morning in Barcelona. The question about train vs. airplane has been answered and I will be purchasing train tickets. I am going to be looking at the small cities suggested and I know it will be difficult to choose. I am glad it was mentioned to have back-up plans for the poor weather. I am not someone who cares to see the bull fighting areas, but the architecture, old town pieces, markets, all would be fascinating. Please keep advising, I'm going to be reading this up until the day we leave. It is helpful.

You're going to need another trip to Spain for sure! The more you read, the longer your wish list will get.

Something that might interest you is the 2-hour Barri Gotic tour run by the Barcelona tourist office. I don't know to what degree the exact itinerary varies with the guide you get, but I enjoyed the history mine imparted as well as seeing a number of architectural bits and pieces I would never have stumbled on myself. You'd definitely want to see some of the Barri Gotic anyway.

You can save considerable time (and money) in Barcelona if you mainly want to see the exteriors of modernista buildings as opposed to the interiors. If that happens to be the case, I'd suggest seeing the block in which Casa Batllo is located (which has two other important modernista buildings) and the nearby La Pedrera. Also take a good look at just about any printed map of the city. A lot of the flagged buildings that are not museums are modernista sights. There may be some in the area around your hotel or near the path you will take from sight to sight. Free sightseeing opportunity! I'm not trying to discourage you from going inside some modernista buildings, but your trip is very short, and each such stop is likely to take about 90 minutes plus travel time, not to mention the 20-25 euro entry fee.

Herewith a few comments about the side-trip possibilities from Madrid:

Toledo: What's most distinctive to me are the scattered mudejar (Moorish-style) buildings that are mostly found in more southern parts of Spain, but the historic area is old, huge and very atmospheric. Tourists tend to congregate in the area around the cathedral and along the path to it from Pl. Zocodover. It's a bit like Venice: wander away from that area and you may be totally alone. It's easy to lose yourself in the back streets, so having a map is a very good idea. Toledo is fairly hilly, so it can take a bit longer to walk from place to place than you might expect just from looking at a map. And did I mention that it is very large? It would give you a full day, for sure.

Segovia: It's more than the aqueduct, though that is a stunning sight. I enjoyed the look of the historic section of the city a lot and just wandered around. I ended up not having time to go inside the Alcazar. The streets are more generally more open than those in Toledo and Barcelona's Barri Gotic, etc.

Cuenca: The hilly old town is sizable but doesn't approach the magnitude of Toledo's. It's built alongside a ravine with houses right up to, or over, the edge. One other distinctive feature is that it has a couple of good modern-art museums. Few American tourists make it to Cuenca (be the first person on your block!), but it's expensive as a spur-of-the-moment day-trip because of the last-minute rail fare. In your situation, I'd choose Toledo (my favorite) or Segovia on a short trip.

I think there is plenty to see in Barcelona, and enjoy it, taking time to sit and look and wander. I suggest day trip:I enjoyed a side trip by train to Tarragona and saw many lovely beach spots passing my window-so many I regretted not planning a side trip to those.
I also enjoyed Montserrat, in a different way ( great geology!) but it is inland and you can do just half a day there and back.

With your schedule I don't see how you fit in daytrips or extra places. Both cities are huge with so much to see and do. Plus a half day of travel between. You really only have 5 days. The good thing about daytrips is that they can be done on the fly, so have a few options that interest you and be prepared. If once you are there, you feel like doing it, go for it. You've been given several good options.

"We would really like to see a small town with some of the famous views"

Which "famous views" are you speaking of? If you tell us (or link a picture), people can suggest the best daytrips.

I agree that in six days, you will want to split your nights between Barcelona and Madrid, and take the AVE (fast train) between them, and then do daytrips if wanted/needed. Do book your AVE as soon as you are sure of your dates, for best prices (they only go up closer to travel, as cheaper fares sell out).

To book the train, you will need to use Paypal as the Renfe site rarely accepts US credit cards, and you will need this detailed tutorial from TripAdvisor: https://www.tripadvisor.com/Travel-g187514-c80518/Madrid:Spain:Buying.Renfe.Tickets.Online.html

Your description of "a small town with some of the famous views" is a little too esoteric. It sounds like a romantic vision of the destination has runaway in your mind, and needs to be tempered with a reality check (through further research) in order to avoid disappointment at the other end.

With only 6 days (or nights ??) at your disposal you really don't have time to add a 3rd destination into the mix. Look for suitable experiences within the 2 big cities, or take a convenient day trip.