but that would allow me to have an experience of the Japanese Alps?

The "Japanese Alps" is a term that is commonly misunderstood. Neither Takayama nor Shirakawa-go are anywhere near the Alps really. You can't see the Alps from either place. Takayama is a large town, in a valley at relatively low altitude. Shirakawa-go is up in the mountains, but not in the Alps - it's in a different range. If you want to actually visit the Alps - ie. the mountains - the most popular places are Kamikochi and the Tateyama Alpine Route, or whatever it's officially called. I've never been to either, but I expect both are very touristy. Getting off the beaten track in the actual mountain range would generally involve some serious hiking.

If you just want to enjoy the central, mountainous part of Honshu, I would recommend Nagano Prefecture, though I am a little biased at the moment because I just got back from a trip there. Nagano's fantastic, with lots of great places: Nagano-shi, which has a few sights scattered around, including some famous, atmospheric shrines way up a mountain above the city; Ueda-shi, which has some lovely countryside nearby; Matsumoto, which has a great castle and a few museums, and terrific views of the Alps if the weather's good; the old Nakasendo route in Shiojiri-shi and the Kiso River Valley, which has a string of old post towns nestled in deep valleys. There's lots more as well, the prefecture's huge. For me, Nagano's more interesting and more beautiful than the mountains of Gifu. But like I said, I'm biased at the moment.

You could also of course spend extra time in Tokyo and Kyoto! You're not going to run out of things to see and do in those cities.

If you have any specific recommendations about "modern takes on traditional Japanse architecture", I would be more than happy to go see that as well!

My favourite building in this direction is the Basho memorial in Iga-Ueno, which was built during WWII. I'd hardly recommend you go all the way to Iga just to see it though! Other things you might want to look out for:

Tsukiji Hongan-ji, in Tokyo: it's a modern take on ancient Indian Buddhist architecture, and a very unique building. Contrast this with the head temple - Nishi Hongan-ji in Kyoto - which has some of the best architecture of the pre-modern (ie. Edo) period in the country.

In Nikko, the Imperial Villa was built as a palace for the Imperial Prince and then the Emperor, and is an interesting example of a traditional palace built for more modern times. It's an eclectic complex, being composed of different buildings from different locations and eras that have been cobbled together to form a single palace.

The State Guesthouse in Akasaka has a modern traditional Japanese luxury guesthouse built to house foreign dignitaries, like Donald Trump. There's also a grand Western-style palace on the site.

Tenri, near Nara, is the head of a large religious sect. They've built a fascinating complex there which includes not only large religious buildings, but also a whole planned town complex.

On the JR Rail Pass question: given the cost of the pass, it's only really Shinkansen and Limited Express trips that are going to help pay for the cost of the pass. It's easy to see where the Shikansen goes, while Limited Express trains generally link larger cities which are not served by the Shinkansen to large cities which are served by the Shinkansen. Some trips - particularly in the mountains - are easier by bus, while heading to somewhere like Koyasan is easiest on private, non-JR trains; but it's not expensive. I've written a whole FAQ on the JR Pass, which I suggest you have a read through.

It is doable in 19 days. But you should fly between BA and Tucuman. If you book the flight in advance it won't cost more than the 20 hour bus ride.

Then go to Potosí in Bolivia (do tour here) go to Atacama desert in Chile then back to Buenos Aires.

It's a strange choice of places. Most people would include the Uyuni salt flats, either going north from Salta via Tupiza, or south on the way between Potosi and San Pedro de Atacama. The jeep tour takes 3 days once you arrive in Tupiza or in Uyuni.

At the end of your trip you can fly out of Calama in the Atacama region, and connect to BA via Santiago.

Hmm, your knowledge of economics would appear to rival your knowledge of Brazil. Leaving aside the meltdown around the time of Plan Collor in the early 1990s the peso has been the weaker currency for decades, something cemented by Argentina’s own economic meltdown at the turn of the century. It’s picked up pace over the past decade. I can recall being in Buenos Aires a few years ago and seeing large numbers of Brazilians holidaying on the cheap. I’d say most of the people in my hotel were Brazilian and even the currency touts on Florida Street had learned a smattering of Portuguese.

I have much book knowledge on Brazil and on South America in general, but I've never myself been there (though I'd like to go one day). So far, in other words, I just have vicarious or armchair experience over there.

When I was stating that the Brazilian currency would be cheaper than the Argentine peso, note that I did not mean in real life. I just meant in a hypothetical world, that is to say if Argentina were a more developed country and didn't have the currency troubles of its own that it has had in real life, while Brazil in that scenario was still more or less the less-developed country that it has been in real life with a lot of currency troubles in the past to go along with it.

Did these particular hotels in Salvador, the year round, cater to Brazilian but also Argentine and Chilean tourists looking for more of a cultural holiday (Salvador being a major Afro-Brazilian hub) or more of a beach holiday?

Frankly, I have no idea what motivated them but the fact that many took advantage of the city tours, the trips to Bonfim, to the turtle sanctuary at Praia do Forte etc suggests that their experience was little different to most other domestic and foreign tourists. Cruise liners stop in Salvador year round too.

Furthermore, the Brazilian real or cruzeiro or cruzado (depending on the era we're talking about) would most probably be a good deal cheaper than the Argentine peso (or at least much of the time)

Hmm, your knowledge of economics would appear to rival your knowledge of Brazil. Leaving aside the meltdown around the time of Plan Collor in the early 1990s the peso has been the weaker currency for decades, something cemented by Argentina’s own economic meltdown at the turn of the century. It’s picked up pace over the past decade. I can recall being in Buenos Aires a few years ago and seeing large numbers of Brazilians holidaying on the cheap. I’d say most of the people in my hotel were Brazilian and even the currency touts on Florida Street had learned a smattering of Portuguese.

You haven't specified when in February, but if it's more than 30 days away then you may be able to book a 1st Class train direct from Colombo to Anuradapura through an online agency. Alternatively you can buy almost-free 2nd class tickets at the station any time before the train leaves, but in that case you'll be competing for seats with people who do the journey regularly, meaning there's a significant chance you'll be out-competed and end up standing for hours in a crowded carriage.

There are bus services but they will likely be crowded.

As a well travelled person in his early sixties who is just finishing a fortnight's spin through the highlights, I recommend installing the PickMe app on your phone and using that to book a taxi when you're ready to leave Negombe/Colombo. The PickMe cost depends on the selected vehicle size and competition, but you'll probably be up for somewhere between 7300 (flex car) and 11000 (sedan car) LKR.

In the wider context of getting around Sri Lanka, there are comfortable air-con minibuses between many places (e.g. Anuradapura to Kandy, Galle to Colombo) that cost 2-3 times the price of the almost-free but crowded regular buses and offer a better chance at a seat. Bear in mind these "expensive" buses cost only about $2 to $4 per seat, so they won't break your budget. You can't book these in advance and their timetables are not published, but you can ask your hotel or just show up at the bus stand and hope one is about to leave.

Let's put it this way, by way of an old joke.

Some years ago Nestor Kirchner was visiting Brazil on a state visit. Lula invited the Argentine president to visit a school where Kirchner asked one of the young pupils to describe how he felt about Argentina.

'We are like brothers!' said the boy

'Really?' said Kirchner, beaming and visibly impressed. 'Brothers not friends?'

'No' said the boy. 'You get to choose your friends'.

Actually, I don't mind Argentina. One of my daughter's godmothers is Argentine. They make nice wine and Buenos Aires has potential to be quite a decent city. I've stayed there on a number of occasions. You just have to forgive them their bad haircuts and appalling attempts at cookery and football.