'I am interested in something that is just invisible to everyone': Tariq Khalil. Credit:RONI BINTANG Khalil was determined to find out the story behind this "mad" house. He learned it was the brainchild of local tobacco baron Haji Samsul, who was intoxicated by the fancy mid-century modern style of houses he encountered on his business trips to central Java. There were no architects in Indonesia - let alone Madura - following the expulsion of the Dutch in 1957. So Samsul made sketches and gave them to local builders, who in 1967 created his dream home. "This - albeit elite - habit soon spread in and around Madura's big towns where builders and owners freely rolled in elements of art deco and mid-century modern," Khalil says.

Khalil has travelled to 50 Indonesian cities and towns in pursuit of mid-century architecture. Credit:RONI BINTANG "Today they would carry an aesthetic health warning," he quips. Khalil is obsessed with this unique but obscure architectural style. Called Jengki (from the word Yankee), it briefly flourished throughout Indonesia in the 1950s and 60s. Jengki is characterised by unusual shapes, such as air vents in playful circles, trapeziums or diamonds. Credit:RONI BINTANG "I feel like a weirdo," Khalil says. "I am interested in something that is just invisible to everyone. It's there in front of your eyes. Every town in Indonesia around in the '50s has this stuff."

When Khalil first came across images of Jengki-style architecture from the Indonesian city of Bandung a decade ago, its "bold lines and outlandish angles" reminded him of The Flintstones cartoons. The aesthetic struck him as unusual but "kind of familiar". A Jengki-style house in Jakarta. Credit:RONI BINTANG Jengki is Indonesia's version of mid-century modernism, characterised by unusual shapes, such as pentagons, asymmetrical roofs, cut-out doors and windows, tilted columns or walls and air vents - crucial for the tropics - in playful circles, trapeziums or diamonds. Khalil was beguiled by the fusion of geometric forms from southern California. A touch of Hollywood - fast-food drive-ins and flamboyant motels - was transplanted to Java. Former Soviet townhouse from the mid-1950s in Kebayoran Baru, Jakarta. Credit:RONI BINTANG

He compares the visual assault to the first time someone bites into a durian - the South-east Asian fruit that has the texture of custard and (some say) a smell like rotting flesh - "something so wrong, but kind of pleasing". "Am I enjoying this or am I not? For me, personally I really liked it." A 1950s revival style fun palace at Blok M, Jakarta. Credit:RONI BINTANG And so began an Indonesian odyssey that took Khalil - whose alter ego is an environmental consultant from Glasgow with a "healthy dislike of travel and no understanding of architecture" - to almost 50 cities and towns, from Sumatra in Indonesia's west to Papua in the east. While working on mining projects he would sneak away and sweet-talk his way into buildings across the archipelago. "Why wouldn't you do something like this in Indonesia, when everyone just opens their doors?"

Apotek Sputnik, a former pharmacy in Semarang, opened the year after the Soviets' Sputnik satellite launch in 1957. Credit:Tariq Khalil Khalil's modus operandi was always to follow the money. "You go to a town and the first thing you do is go to Chinatown. Where are the traders? Where are the shop houses - all those ugly ones with the metal grilles and the battered tiles? They were once very, very beautiful. Around there, you are going to get some of the [mid-century] stuff that might still have survived." The Apotek Sputnik in Semarang, on Java's north coast. Credit:Tariq Khalil In South Jakarta, Khalil once taught a maid to cook Indian food in exchange for cutting down trees and hedges to photograph a diplomat's '60s townhouse.

In Semarang, a port city on the north coast of Java, he paid street vendors to move so he could photograph Apotek Sputnik, a former pharmacy with space-age windows and a rocket-cum-satellite above the door, that opened the year after the Soviets' Sputnik satellite launch in 1957. 'It should really be a bar': the Apotek Sputnik's eccentric interior. Credit:Tariq Khalil Once a manufacturer of powdered drugs - the supply of Western medicines dwindled after the nationalisation of foreign pharmaceutical firms in the late 1950s - Apotek Sputnik served an elite lifestyle now usurped by pharmacy chains. "The Sputnik is a bizarre relic upstaged by street carts. It should really be a bar," Khalil notes sadly. Semarang, an important colonial port city, is prime hunting ground for Jengki style, given its history of sugar and tobacco plantations. "These commodity barons all wanted to have a house up in the hills, a mansion, a townhouse in the city."

A sketch community group, Orart Oret, researched the influence of Jengki as part of a biography on one of the pioneers of the style, Oei Tjong An, who once built a house in Semarang with windows at the bottom. "A fellow architect questioned why the windows were at the bottom when they served no function," says Adeline Gunawan, who heads the research division of Orart Oret. "But Tjong An said they were beautiful and artistic." Unfortunately the bottom-windowed house, which sounds like something from a Dr Seuss book, has been demolished and replaced by a bank. Gunawan worries Jengki-style homes will disappear altogether if owners can't afford the maintenance costs or choose to demolish them. "The government must get involved in preservation efforts," she says.

"Our research went for two years. Every two weeks we wandered around to look for Jengki houses which were in good condition and we preserved them by way of drawing." Jengki-style architecture is widely regarded as an expression of political freedom following Indonesia's proclamation of independence on August 17, 1945. Some have even speculated that the pentagon shape in many of these buildings was inspired by the Indonesian state ideology of Pancasila, which has five principles including a belief in one God, democracy and unity. Gunawan says the unique style was a form of rebellion against the "neat, well-structured" buildings of the former Dutch colonialists. "Being nationalists … they created buildings without any rules, asymmetrical. Perhaps some people called it norak (tasteless) but then that style became popular as Jengki."

The irony of this nation-building exercise, according to Khalil, was the Jengki-style prototype was designed by Dutch architects and engineers, who were delivering endless projects from 1949 to 1957, "somehow oblivious yet making hay" inside the first president Sukarno's post-revolutionary hothouse. "They [the Dutch] know the game is up, so they go for this last flourish and it's a crazy flourish. They weren't really welcome here, right? They just fought a bloody war. I like to call it the twilight Indies style. It is architecture for an extreme period." They built Indonesia's first garden city in Kebayoran Baru, now one of the most affluent areas in Jakarta, with magnificent villas for executives from international firms such as Batavia Oil, Shell's main oil-producing entity in Indonesia. "It was supposedly a new Indonesia for Indonesians, but it was the exact opposite," Khalil says. In 1957 the Dutch were finally forced out and their assets nationalised. But Indonesia suddenly found itself without architects.

Much of the design work was taken on by builders and contractors to the Dutch, or sometimes students from the Bandung Institute of Technology, who were influenced by American architecture. "Now this Jengki stuff goes viral, gets madder and madder and becomes the standard form for success and luxury," Khalil says. He was surprised by how little had been documented. "Talking to academics, no one really knows about its risky rags-to-riches history. The way to set the record straight was to go back to the owners. The only archive I ever found was in Holland, in Rotterdam. I went to Rotterdam and interviewed an 80-year-old Chinese gentleman, one of the interns who built these houses." As the distinctive buildings slowly disappear across the archipelago, victims of neglect and disinterest, Khalil has immortalised them in a new coffee-table book, Retronesia: The years of building dangerously, available from this week via Amazon Prime.

The "dangerous" vacuum was filled by the late 1960s, as Indonesia's first wave of homegrown architects began rolling out sober styles of architecture championed by Sukarno. "As these architects would say [Jengki] is form over function, it is superfluous, it is too flourishy," Khalil says. "The verve was gone, right? There was just earnest mission: 'We are here to build the country'. What they went on to make was pretty boring." A remarkable period of architectural creativity in Indonesia was over. With Karuni Rompies