The Cubana flight is an introduction to so much about Cuba: a touchy-feely culture where the steward unselfconsciously holds your hand and shoulder while asking what you want to drink.
Santiago's Hotel Casa Granda is the town's main spot for those who can pay in dollars: half the tables have middle-aged white tourists seated with young black women, all uniformly good looking, who seem to be companions for the visit, not just the evening. The most distinctive dish is rice and black beans, still called by its pre-political correctness name Moros y Cristianos (Moors and Christians).
Visit the house of the professor who invited me to the country: an extraordinary area of decaying and decayed bourgeois mansions (the original Bacardi mansion is said to be on one of these streets). But the houses now have bright neon lights and little furniture. My host is very black and from a large family of academics, surgeons and engineers.
Apparently race is seldom openly discussed in Cuba, but it is hard to ignore the fact that it is basically a black/mestizo society run by white people, from Fidel Castro down.
The conference ceremony has a chorus of young red-scarved pioneers, boys and girls, who give us a patriotic anthem in which Castro certainly figures.
Cuban TV seems to consist of old US movies and local talkathons conducted by officials: youngish, well-dressed, often long-haired like leftover student radicals, and usually white. The current one is banging on about cultura and humanidad , and how Castro saved the country from prostitution and corruption. This is a bit hard to square with the busy hotel terrace and the mysteries of the three parallel currencies, a system that ensures a visitor can never get to spend a peso. One could feel that Marxists have lost the meaning of "objective contradiction".
Havana is a wonderful mixture of museum and East European bomb site, but nothing prepared me for how grand it all must have been, and probably will be again. And yet the streets are full, and there is music everywhere: in the lobby of the hotel Ambos Mundos a woman plays show tunes at a grand piano, while a wire-cage lift carries the faithful up to room 511, where Hemingway's typewriter sits on his desk in his regular room for ever.
A taxi driver tells me he is a sociology professor, but makes ten times his salary from three nights' work. Anyone who can get near a tourist is doing well, but most people cannot. British colleagues said to me "ah, but they have their health service", but so do Mexicans and a Mexican colleague here was horrified to be treated by beggars as a rich westerner. In my hotel, magazines press the availability of Cuban hospitals for cheap but high-quality operations for dollars. It sounds a little familiar, a final self-contradictory spasm in a failed model of public heath provision. Discuss.
At the airport the lines to get out are long, slow and randomly entered by military officials; no one protests because, natives or visitors alike, they know there is no defence whatever against arbitrary action. It is a sad last memory after all the good things.
Yorick Wilks is professor of artificial intelligence, University of Sheffield.