It was torture with a creative flair -- build tiny cells that kept prisoners from sleeping, sitting or pacing, and decorate the walls with mind-bending art.
These chambers operated during the Spanish Civil War of 1936-39, and were the work of communists fighting for the government side as it battled troops under fascist Gen. Francisco Franco. Their existence is a bizarre, little-known footnote to the conflict, and is now the focus of historians and artists.
Researchers say the Soviet-inspired cells were the size of a walk-in closet, with terra-cotta bricks sticking up from the floor at sharp angles. A cot and a seat attached to the walls teased prisoners with the lure of rest, but tilted so far downward they were useless.
One wall was curved, and others were painted with circles, cubes, slanted lines, spirals, checkerboards and other shapes. By night a blinding red spotlight made it all appear to move and pulsate. Sense of time and distance crumbled.
The light of day filtered through a window dyed green -- the color these tormentors thought best for gutting a man's spirit.
"Just seeing the inside of a cell is enough to make you dizzy," said Cesar Vidal, a historian who has written extensively on the war. "I imagine that if you were in there for days you could go mad."
He estimated that several hundred people spent time in the cells, used to extract confessions or extort money.
Art historian Victoria Combalia says the dungeons have been largely ignored through the decades, like many of the war's grim reminders, because this patch of Spanish history is so touchy.
Older Spaniards have painful memories of the war and its desolate aftermath, and Spain's transition to democracy in the late 1970s included a tacit accord to stay mum about atrocities on both sides. Human rights groups have just recently begun digging up mass graves of civilians executed by Franco loyalists.
"Any Spaniard knows that we are only now beginning to study the war in a more objective way," said Combalia, who has written about this case of abstract art as an instrument of suffering.
Detention centers housing claustrophobic cells existed in much of government-held Spain, and Madrid alone had more than 200. But only a handful boasted painting on the walls, all in Barcelona. One worked out of a church.
Combalia, who teaches at the University of Barcelona, traces the art to the Bauhaus school -- which emphasized simple, functional designs -- and painters such as Paul Klee and Wassily Kandinsky.
In the 1930s, Klee, Kandinsky and others were at the forefront of a movement in which artists studied the psychological effects of color and shape. Bauhaus teacher Johannes Itten believed colors had intrinsic characteristics that directly affected how the viewer felt.
"Color is life, for a world without color seems dead," Itten wrote in "The Art of Color."
Klee expressed himself with simple lines and symbols, and once described his early work as "taking a line for a walk."
The lines and colors on the Barcelona cell walls and the Kandinskyesque circles point to Bauhaus inspiration, Combalia said. "The similarity is striking," she said.
The detention centers that housed cells with or without art were known during the war as checas -- from the Russian acronym for the secret police that preceded the KGB.
An apparent key figure in the artful cells was a double-agent Frenchman named Alfonso Laurencic. A Franco-era account of his trial in 1939, after the war, describes him as a musician and painter who actually designed the cells.
The idea of using abstract art to torment people, Vidal said, stemmed from Soviet advisers aiding the Spanish communists who came to dominate the government, or Republican, army in late 1936. One torture victim, Martin Ingles, wrote about it in a book published in 1940 under the title "In the Grips of the SIM." The SIM was the Republican intelligence service.
Ingles, a civilian who lived in Barcelona, said he was thrown into a cell and denied food for days. He couldn't pace or sit down, just stare at the shapes on the wall.
"Then, on the sixth day, something strange happened," he wrote.
"The movement of the lines and the way the cubes stood out created such a perfect sense of reality that I would throw myself at the wall with clenched fists, trying to stop the former and touch the latter," Ingles wrote.
A life-size replica of a checa, created by Spanish artist Pedro G. Romero, was featured at a recent contemporary art festival in Madrid.
Romero's work was discreetly labeled, and from the outside looked like a wooden garden shed. Many people ventured inside for a peek, even lining up to do so, but few knew what a checa was, said Miguel Pedrazo of the museum that sponsored the exhibit.
One clutch of college women went in one by one and came out reeling off nervous giggles -- it does get spooky in there -- oblivious to what they had seen.
Some visitors thought the chamber was a sauna, Pedrazo said. Or a labyrinth. Anything but a miniature house of horrors.
"When they heard what it really was," he said, "their faces would drop."