Tie. Cabo San Lucas in 1983, coast of Michoacan in 1984 the year after the road was built. That's right I'm one of those old worn out "you can't see what I saw" loudmouths.
The former was gone within months of the direct flights starting up a few years later.
There's actually a diorama of it on the Internet but I'm too lazy to look it up again. Kilometer two was the eastern edge of town. Evenrthing was open coastline from there to San Jose. Kilometer twelve was a free pirate campground known to vagabonds and free spirits worldwide. (Even though it was more than cool to sleep right on the beach in the harbor downtown. And you were closer to the natural firehose that was their historic freshwater spring too. It still gushed right out into the streets back then.)
You had a real hard time spending more than Three Dollars on a meal with drinks. And they had a beautuful clean boat that took you to Puerta Vallarta three times a week for $5 including cabin. This is the Cabo that John Wayne saw in the 1950s with some pretty cool improvements.
The latter is the only place on earth that I ever went back to deliberately and it had already changed a lot in just two years. Pretty scary place right now too, I suspect.
But in '84 you had big freshwater steams coming down into the ocean and not even a game trail going up them. I'll never forget that and I have no expectation of seeing anything like that again. Two years later those were already jeep trails. Mexico's Big Sur.
Curiously surfing shrine La Ticla was an epic party the first time (January,) and deserted the second time, (mid November and sweltering.) We were the only gringos in town period. I did get to meet a direct descendant of the "we don need no steeking badges" guy farther south and that area is also one of two remote places I know of where bad things have happened to passersby for decades at a time, the other being McBride, BC. This even though you will usually go through four military checkpoints between there and Acapulco.
Been all over the West pretty much from Prince Georfe to Panama, Spain, France, Blue Ridge Parkway in the Fall, went to college in New England, been all over the Canadian Maritimes and Pacific Coast as well. Vancouver was pretty choice back in the day if you like the big cities.
Places I expect to try and try to pull > 1 month stints in before I check out: Salto Argentina, Equador (just to visit at least, palm trees at 9000 feet,) Galacia.