A FEW MORNINGS LATER, at 4:20 A.M., I boarded an Ilyushin turboprop, the finest 1960s technology, for a smoky, rumbling flight to the eastern province of Holguín. A thundering salsa band greeted our 7 A.M. arrival, and the other passengers—European tourists—boarded buses to local beach resorts, said to be the most luxurious in Cuba. In a dusty parking lot, I negotiated for the front seat in an old Toyota jeep headed to Moa Bay, said to be the most polluted.

It is also one of the most remote. For ten dollars—three times what the five Cubans in back were paying—I got the front seat during a three hour drive east. We climbed into the Sierra del Cristal, one of the most pristine places in Cuba, land of small streams, hidden groves of palm trees, tight valleys alternating with long vistas. Just four years ago a farmer discovered an "extinct" mammal, the groundhog-size almiqui, rooting in his crops.

The mountains gave way to the farming plains where Fidel himself grew up. Now it was more Marx Brothers than Marx: abandoned farms, bulldozed trees, cattle ranches with more cowboys than cows, and a horse-breeding station that, the driver assured me, had only one horse. Cuba in a nutshell. By the time I made it to Moa at midday, I'd traded the Toyota for a Nash Rambler with a squealing piglet lashed to the bumper. In the back of a bicycle rickshaw, I went looking for the underground environmentalists.

This was slow going at first. The chain on this three-wheeled contraption kept slipping loose, and the driver would pedal forward, then remount the chain by pedaling backwards. We lurched down Moa's main street in this overtly symbolic manner ("That's Cuba!" some bobo shouted) to a humble wood house tilted over a dirty creek, the home of Silverio Herrera Acosta, an asthmatic 55-year-old photographer. With him was Francisco Hernandez Gomez, a young-looking 36-year-old activist. These two were it, their own tiny movement, without even a telephone yet subject to repression and arrest.

For all its green gains, Cuba is still a police state, as the island's few independent environmentalists are constantly reminded. Opposition ecologists and amateur greens who try to organize or protest can face an escalating menu of retaliation: career coldness and lack of promotions, followed by lecturing, then threats, then informal and formal detentions, all the way up to serious jail time. The founders of Naturpaz, a tiny, illegal group in Havana, have been arrested repeatedly for advertising the state of the filthy streams and streets in their slums. Cuba's real environmental policy, Silverio told me, is "Shut your mouth." Fidel's conservation initiatives are like "a woman who puts on makeup but doesn't bathe."

Silverio and Francisco had become activists only because Moa required it: An American company, Freeport Sulphur, built a refinery here in the 1950s, when this area was still wilderness; now Cuba operates three Soviet-built smelters—known collectively as the Che Guevara complex—and leases the American refinery to Sherritt International Corporation of Canada (which says that it does its heavy refining elsewhere). In a fit of central planning, the town of 65,000 workers was built directly downwind, and the result, Silverio said, is an epidemic of asthma and one of Cuba's highest lung-cancer rates. ("Even teenagers get it," he said.) He wiped a finger across his glass coffee table, bringing up a black smear. "I cleaned this yesterday," he said. "It's a residue of hydrochloric acid, caustic soda, ammonia, and others."

Francisco tried going through the proper channels. He wrote a letter; a government team came and looked at the nickel dust; he never heard another word. "You can protest to the government," Francisco said, "but it's just for your own pleasure."

In 2006 he started to organize a survey of asthmatic children, but the police came to his house four times, he says, warning him to stop. That June, he claims, he was attacked and beaten by government sympathizers and, when he tried to start the survey, summoned to police headquarters, where he says he was kicked in the head, back, and kidneys. Almost a year later, he pulled up his Puma T-shirt and showed me a long white scar.

Francisco and I were crossing an intersection when he shoved me into the bushes. A motorcycle cruised past slowly, the rider wearing an orange helmet.

"That's the guy who watches us," Francisco explained. "We aren't afraid of jail," he added, with more resignation than bravado. "If we have to go to jail, we'll go."

We went to the refineries instead. We hired a thundering 1950s wagon and rode through a landscape out of Road Runner v. Coyote, with red earth, yellow sulfur deposits, and clouds of billowing steam. Earthen berms made it difficult to see anything, but later, Eudel Cepero, an exiled Cuban environmentalist who was teaching at Florida International University, steered me to the coordinates on Google Earth. From outer space I inspected the pockmarked minescape, its gigantic slurry pools spilling plumes into the sea. This too is Castro's environmental legacy.

I had to get out of Moa. All three hotels rejected me, the daily buses had gone, and there were no cars for hire. At nightfall Francisco walked me to the highway outside town, where I waited until 11 P.M., one of 30 people in the dark hoping to flag down a ride. Finally, the patient Francisco suggested I sleep illegally at his house, even though "the captain will send men to beat you." We walked home—zero carbon emissions—and before midnight arrived at the three-room house he shared with his wife, brother, niece, and mother. The mother sat in the front yard, in a rusty dentist's chair, smoking a cigar. I took a Cuban shower—a bucket of water, a cup, and a rag—and lay down on the family's best bed, a coil of taut ropes punctured by broken springs. Mosquitoes, breezes, and finally rain blew through the boarded walls.

Screw the resorts anyway: This was the Cuba I loved, generous and striving, principled and poisoned, hotheaded, barefoot and stubborn, stirringly alive. No amount of cynicism (or accuracy) can overwhelm that romantic mix of Cuban genius and chaos, mythology and self-contradiction.

I lay on Francisco's rope mattress for the next hour, too exhausted to sleep, counting glass bottles. Like all Cubans, his family carefully washed and reused them, and there were 42 stacked in the corner. Cuba is less a sustainable society than a pre-consumer one. Everyone walks or rides everywhere. Dumpsters are empty, because virtually everything can be fixed, sold, or traded, or fed to pigs. Paper is rounded up by old men on the state payroll. Everything from kitchen greens and eggs to pork rinds and table fish is gathered so slowly and so seasonally that it would make even a devout locavore swim for Key West in frustration.

Only necessity has made Cuba green, which may be the island's real lesson: No transportation. No shopping. No advertising. No energy. No waste, no fat and no gristle, no conspicuous consumption, and not much inconspicuous consumption either. Non-economy is green economy.

Eventually Francisco brought me a nightcap that knocked me out. It was a glass of water, reeking of sulphur.