This is just one of the venues of "documenta", one of the world's biggest and most ambitious contemporary art fairs, which takes place every five years and which opens on Saturday.

This year's fair is the 13th documenta since its founding in 1955 by an artist banned by the Nazis and showcases the work of participants from some 56 countries, including Britain's Tacita Dean and South Africa's William Kentridge.

Carolyn Christov-Bakargiev, the festival's artistic director, said she wants to broaden documenta's focus from the visual arts to culture at large, ranging from quantum physics to historical artefacts.

A U.S.-born Italian-Bulgarian art historian with a distinctive mop of tightly curled golden hair, she dislikes categories and has frustrated some by providing no over-arching concept for the exhibition, preferring a "holistic" approach.

"Documenta is dedicated to artistic research and forms of imagination that explore commitment, matter, things, embodiment," said Christov-Bakargiev, during an academic lecture she gave instead of the traditional opening news conference.

One key theme that she said had emerged, however, was that of collapse and recovery, appropriate for a show created to revive both the visual arts in Germany and the city of Kassel, which was devastated during World War Two.

Originally modest in size, documenta's budget is now around 25 million euros, and artworks are shown throughout the city in parks, museums, cinemas, and the train station, "like an exploded museum", according to Christov-Bakargiev.

Documenta is one of Europe's top four exhibitions, alongside the Venice Biennale, Art Basel and Monumenta in Paris, and takes pride in its avant garde image. In 2007, China's Ai Weiwei brought 1,001 of his compatriots to Kassel as "live exhibits".

Some 750,000 visitors are expected for the 13th documenta. Kassel has around 195,000 inhabitants.

Reflecting the original ambition to re-imagine and revive culture, the exhibition casts its net this year as far as the Afghan capital Kabul, also destroyed by conflict, where documenta has a separate venue and series of seminars.

An artwork commissioned for documenta draws the parallels between the two towns. "A Brief History of Collapses" juxtaposes two films taking us on journeys through Kassel's 18th century museum the Fridericianum and Kabul's Dar ul-Aman Palace.

Through other artworks too, documenta depicts Kabul not simply as a place of conflict but also as home to a rich cultural heritage and potentially a future hub of creativity, "through acts of radical imagination".

HITLER'S BATH

The ability to re-imagine the world is a golden thread running throughout the exhibition and linking the work of artists with that of participating physicists, biologists, anthropologists and a hypnotherapist.

"The boundary between what is art and what is not becomes less important," said Christov-Bakargiev.

One exhibit displays a series of high-tech experiments in quantum physics including "Entangled Photons: Einstein's spooky action at work". Researchers from Vienna University, somewhat out-of-place in their conventional attire among all the bohemian hipsters, are on-site to explain their meaning.

"At first it seems like just a scientific experiment," said Bernhard Wittmann, a PhD student, standing in front of a blackboard scribbled over in chalk. "If you look closer, though, you see it presents a different way of viewing the world."

"The arts and sciences should collaborate more," he added. "We learn from talking with artists, and they learn from us."

Christov-Bakargiev, previously director of Turin's contemporary art museum, has said she is not sure museums will continue to exist in their present form.

Documenta sometimes feels more like a Wunderkammer, or room of marvels, than a contemporary art show.

This is epitomised by the "Brain", a small space in Kassel's 18th century Fridericianum museum full of objects, artworks and documents, "a miniature puzzle of an exhibition that condenses and centres the thought lines of documenta as a whole".

There you can find paintings of vases by the late artist Giorgio Morandi on display alongside the original objects.

Nearby, the visitor can see photographs of artist Lee Miller taking a bath in Hitler's onetime apartment in Munich, alongside some of the artefacts she found there. These include a towel with Hitler's initials and Eva Braun's face powder compact.

'DOGUMENTA'

Sustainability and the relationship between nature and culture are also strong themes of the documenta, which some have jokingly dubbed 'dogumenta' due to its interest in dogs.

"Many think there is a difference between culture and nature but there really isn't... It is important to gain a perspective on the world and on life that is not just human," Christov-Bakargiev told Zeit magazine, criticising anthropocentric views.

Christov-Bakargiev, whose fluffy white pooch Darcy rarely leaves her side, has commissioned a vet for the exhibition to discover what dogs find "beautiful" and has set aside a "dog park" in Kassel for the use of canines.

On sustainability, documenta exhibits the work of U.S. artist Amy Balkin who is lobbying UNESCO to recognise the earth's atmosphere as a natural World Heritage Site.

She displays requests signed by Christov-Bakargiev and sent to 186 UNESCO member countries, asking them to support the proposal. Visitors to the exhibition are invited to sign ready-made postcards petitioning for the site.

Documenta will run from June 9 to September 16.

(Editing by Gareth Jones)

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