Argentina, Chile, and Machu Picchu

Iguazú falls require 1.5 days on the ground to see it all: 1 day for Argentina side and a few hours for Brazil side. Some nationalities require a visa or need to pay a fee to cross into Brazil, so check that. A tour will help with the cross-border logistics, but I do not have current info on tours.

Mind that Buenos Aires has two airports. Ideally you will want to fly out of EZE as you arrive, and back into AEP when you return to Buenos Aires. I would allow 3 full days for a taste of Buenos Aires, and more days won't go to waste: there are not that many "blockbuster sights" IMO, but it is a large city with many charming neighborhoods that are far apart.

Santiago is of limited interest to me (and definitely worse in my 2023 visit than in my previous one ten years before). If the cruise wraps up with a visit of Valparaíso, that could be good enough. The nearest highlights of Chile lie either 1,500 km to the north (Atacama) or 800 km to the south (Los Lagos), but spending time in either region would involve a difficult journey to Cuzco for Macchu Picchu.

Speaking of which, there is more to Peru than Macchu Picchu: could a future trip to Peru be on the cards? It would make things easier for you.

We have been to South America several times and our favorite countries are Peru, Chile and Argentina.

We didn't do the trip to the falls, so I can't help you there. However, we did do the Cruise around the Horn from BA to Chile in Jan 2014 and it was wonderful. We spend five days in BA prior to the cruise. There is much to see in BA, but warning is that you need to avoid some areas of the city. Ask you hotel or BNB manager to advise you an where to avoid.

Do go to a Tango Show, there are several to choose from and they are wonderful.

The cruise around the Horn is wonderful and the many ports you visit are all different. Be sure to research each port and take the best excursions that suit your fancy. Santiago is a very nice city and worth 2-3 days. Be sure to go up the Funicular that goes up the mountain overlooking the city.

Peru is fantastic and getting to Machu Picchu starts in Cuzco, which was the ancient Incan capital. To reach MP, you will be taken thru the Sacred Valley, which has many great ancient sites to visit. You will take a nice train into the city near MP, where you will likely spend the night.

MP is amazing and you will need good walking shoes or boots to negotiate the hills there. The city is 90% preserved and the ancient stone walkways require a bit of care to negotiate. We did MP on a separate trip in 2019 and we were both in our early 70s. We both are active, but climbing around MP for several hours was tiring.

The altitude is a factor, especially for us, since we live at sea level. We took altitude sickness prevention pills on the trip, but still the altitude will be a factor when climbing the hills.

Not sure if you are visiting Lima, but it is a great city and lots to see there. Again, there are areas to avoid.

If you fly from Santiago to Peru, you will probably have to go through Lima instead of a direct flight to Cusco.

Dining in South America is a very pleasant experience. Each country has different cuisine. All have the Spanish influence, but still there are major differences. Argentina is a beef oriented place and the steaks there are the best ever. Also, check out the beef empanadas. Chile and Peru are on the Pacific coast and seafood is much more of a focus of the cuisine. Have some Chilean Sea Bass and some empanadas with cheese and crabmeat.

Peruvian dining is special. The potato comes from Peru and when you get a meal with potatoes, you get several different types of potatoes. They all have different colors.

We spent a week in Buenos Aires before flying to
Bariloche and did the Lakes Crossing to Chile, a terrific experience. We did not go to Iguazu Falls. We have seen many waterfalls and they are not high on our lists of interests.
We explored quite a bit of Chile too including Santiago, Valparaiso and Zapallar, Chile’s Santa Barbara.
Stay in the lovely Recoleta neighborhood of Buenos Aires not in the city center. This is not only for charm but safety.
In Chile make sure you visit Valparaiso! Go up in the neighborhoods in the hills with all their variety. Fun!
We spent about three weeks on this visit to South America.

I went to Iguazu Falls with a couple friends about 10 years ago. There was no need for a tour company and it did not require extensive planning. We stayed on the Argentina side. We flew from BA to Iguazu and then from Iguazu to Salta in the north.

I used the Lonely Planet guidebook for Buenos Aires. It had highlights of places to see and eat in various neighborhoods, which was useful. It looks like there may not be an updated BA book but there is a fairly recent LP Argentina book. La Boca, Ricoleta, Palermo, the port, and the central city neighborhoods are good areas to see. I was there for a conference at the university so I stayed in walking distance of UBA which was fine but not an advantage for you.

We were in Buenos Aires last February (stayed recoleta neighborhood) and loved it. We flew to Iguaza Falls, spent two nights, saw the falls from both sides, hiked and took the get wet boat ride-- all wonderful. We finished our trip in Santiago and I've got to say the city looked a little worse for wear. After the protests, lots of boarded-up buildings still remain.

Cusco is around 11,000 feet while Machu Picchu is just below 8,000 feet of elevation. We live at sea level and noticed the elevation in Cusco to be a bit of an issue, especially for my husband. Hubby had a headache and moved slowly while I was ok. Machu Picchu being 3,000 feet lower was no problem for us. Walking up the stepped hills in Machu Picchu definitely can be strenuous for many due to the steepness and elevation, but you don’t have to do this to get a real good feel for the city.

We loved Buenos Aires and Santiago de Chile. In Buenos Aires we stayed at the Scala Hotel in the San Telmo area and throughly enjoyed it. San Telmo is a working class area, but we felt perfectly safe and walked most everywhere. In Santiago we stayed at Hotel Plaza San Francisco and enjoyed it too. Both hotels were in good locations for walking around and exploring the cities. If you decide against Iguazu Falls, consider taking the ferry from BA over to La Colonia, Uruguay for a day trip.

For Machu Picchu, it was a National Geographic tour strictly because of all the transportation changes, reservations, etc. it was easier to let somebody else have to deal with it.

The links are to photos of our trips. You can see where we went and they may give you some ideas of what’s there.

I've been to Buenos Aires and to Machu Picchu.

For Buenos Aires, we treated it similar to how we treated any other big city visit - reading guidebooks, picking out highlights, and making sure we had a framework to work from. Also like most trips, we walked around the city - a LOT. It really is fun just connecting dots and stopping along the way to see or do non-planned things. It's been a little while since we were there (2015!), but the main things I remember doing were a couple free walking tours (great way to get your bearings), the Teatro Colon (beautiful), the Recoleta cemetery, wandering the Retiro, visiting some local markets, wandering to le Boca, checking out the colorful graffiti art all over, and then the historical Plaza de Mayo where the mothers of the "Disappeared" protested that dark period, and the church where Pope Francis was Archbishop before becoming Pope.
Really, it was a vibrant and fun city to visit. And plenty of good food at a reasonable price. We'll go back again for sure.
Some have mentioned key things to know about visiting Machu Picchu (2013 for us) and those are the altitude and the hills in MP. You will be at high elevations, and some folks do struggle with that. I remember seeing folks in our hotel with oxygen canisters, so can hit hard for some. It had no noticeable affect on me, except that you do notice breathing harder for any exertion level. If you've been to some of the higher spots in Colorado, you'll have felt it. I wouldn't worry about it unless you have other underlying issues with heart/lung/circulation and would merely add it to the "watch out for" category. Machu Picchu's bigger challenge vs just altitude was the steps up and down and up and down to get to the various viewpoints that give folks the "postcard" photos. It's a relatively large area of ruins to wander through, and it was definitely a leg workout if you spent several hours exploring. Well worth it, but just remember to pace yourself and to expect to do some steps (often irregular and in differing degrees of quality/wear).
Sadly, most of my info is so out of date (and buried in notes somewhere) that I don't have any good specifics to offer other than HAVE FUN! And enjoy seeing a bazillion penguins.

Despite pills, we could only climb ten stair steps in Macchu Picchu without pausing. Everyone responds differently to altitude. MP is a very remote location, with much travel "overhead." It's not like adding one city to a trip in France. Everyone, rich and poor, has to use a shuttle bus from Aguas Calientes to the summit. We chose a tour that included the fabulously expensive and unbookable tiny hotel on the summit.

Can't speak to the Argentina/Chile questions, but I'd suggest that Machu Picchu is not a "stop on the way home" situation. There is no fast way to get to MP. There is no airport nearby to MP, so you have to fly to Cusco and take a 3-ish hour train ride to the town closest to MP (Aguas Calientes). It looks like there is one direct flight from Santiago to Cusco a couple days a week. However to return to the United States you will have to fly back through Lima. Depending on your home airport, many of those flights leave at unholy hours (mine left at 1 a.m.)

I also recommend seeing some of the other sites in Cusco and the Sacred Valley (Pisac, Ollantaytambo, Moray, Saqsaywaman, Maras Salt Mines). It would be such a shame to miss all of that amazing history and scenery as you get to MP. A tour company would make it a lot easier - I personally would have found making my own arrangements very challenging. And a tour company is going to make sure you actually get in to MP while you're there - it can sell out due to visitor limits. I used GAdventures tour but they don't offer any tours shorter than 4 days. Hopefully someone will have another suggestion.

[Can't speak to the Argentina/Chile questions, but I'd suggest that Machu Picchu is not a "stop on the way home" situation. There is no fast way to get to MP. ]

Right - we know that, but our status at this point in our lives is "Retired and Wandering", so "on the way home" can mean many things. In this case it just means "between Chile and the US", and I know there's not a quick, easy way to get to MP. But it's possible that we won't be this close again, so I'm going to see if I can make it work.