We're referring, of course, to the Venice Biennale, whose 53rd edition opened earlier this month to the usual festive crush of art world insiders - collectors, curators, dealers and critics. The Russian billionaire Roman Abramovich was there, entertaining in his 115-metre yacht; French billionaire Francois Pinault, who over the past 30 years has assembled the world's largest contemporary art collection (2,000 pieces, more or less), opened his new showcase in the Punta della Dogana, the former customs house newly refurbished by Japanese architect Tadao Ando.

In the presence of such ostentation, the outpouring of hospitality by the Flemish Community, this year's sponsors of the Belgian pavilion, and by Flemish art dealer Guy Pieters (who flew in the band Zita Swoon to set the tone for the party he threw on the Lido) seemed downright modest. Understated, too, (in comparison) is the exhibition staged by Flemish lifestyle/interiors magnate Axel Vervoordt in the Palazzo Fortuny, named after the early 20th-century textile and fashion designer who once lived there. In-finitum contains roughly 300 works by 140 artists, juxtaposed to emphasise formal and conceptual relationships bridging vast divides in time and space.

Eastern philosophy and Western aesthetics converge in works by artists famous and lesser-known, and intriguing associations arise. One particularly engaging subgroup points to the suggestive power of unfinished images: paintings left in various states of incompletion include a 16th-century Italian Crucifixion, a landscape by Cézanne and the ghostly image of the back of a woman's head by contemporary Flemish artist Michael Borremans. All invite the viewer to wander into their unclearly defined regions.

Vervoordt's show is one of the Biennale's 44 official "collateral" events. Sponsored by institutions and individuals, they are held all over the city. But the Biennale's core is in the Giardini, where the permanent national pavilions and part of the centrepiece exhibition are situated. That show is optimistically titled Making Worlds, hinting at the fact that our own is in need of renewal and that artists almost by definition propose alternative realms or modes of being in this one.

Oddly - and disappointingly for visitors bent on making new discoveries - many of the most striking works are by-now historic 20th-century precursors: the Gutai group, Oyvind Fahlstrom, Tony Conrad, Lygia Pape. Granted, this perception may be unduly influenced by the bias of familiarity: time will tell.

The largest installation is "Human Being", a sprawling, multi-media piece by Cameroon-born Ghent resident Pascale Marthine Tayou, who has created a darkened village of huts on stilts surrounded by mounds of earth, grains, powdery substances (representing cocaine?) and ritual objects, all engulfed in cacophonous sound. Films projected on the walls of the huts show facets of life in African villages, as well as people at work in other cultures, fabricating goods to be sold in the global marketplace - humans linked at the very least by commerce.

Belgium's was the first foreign pavilion established in the Giardini. Designed by Brussels architect Léon Snyers and built in 1907, it is put at the disposal of the country's Flemish and French-speaking Communities in alternate biennial years. This time it's the Flemish, and their choice is a new project by Jef Geys, a much-admired artist's artist from Limburg province, who famously shuns the art world and whose work is as materially modest as it is acerbically critical, multidisciplinary and enmeshed in real life.

For "Quadra Medicinale", Geys recruited acquaintances in four cities to find, document and research the medicinal properties of 12 plants growing wild in the urban environment within one kilometre of their homes or workplaces. The results are displayed - maps, photos, pressed plants and texts. It is all intended to be published in edible, digestible printed form (the technology is not yet available) as a practical survival guide for homeless city-dwellers.

Geys' ethno-botanical exercise is a model that can be carried out in any city, a project with counter-cultural, human appeal. But it was evidently of limited interest to the majority of art buyers at the Biennale, who waited in long queues to enter the US, Dutch and Scandinavian pavilions but mostly bypassed the Belgian.

No such slight was suffered by the well-publicised collateral projects of Wim Delvoye and Jan Fabre, Flemish artists with stronger followings abroad, they each say, than at home. Fabre was the first living artist to be given a solo show at the Louvre (in 2008). Delvoye, witty and subversive, shot to international fame with "Cloaca", a complex machine designed with the help of scientists to mimic the functioning of the human digestive tract. He followed that up by establishing a pig farm in China, where he could tattoo the animals without legal or other recriminations. (He sold the flesh as pork but marketed the decorated hides as art.)

Delvoye's "Torre" at the Peggy Guggenheim Foundation on the Grand Canal, carries the artist's recent interest in Gothic form and ornamentation to new heights. Between sculpture and architecture, the 10-metre-tall steel tower is but a fraction of the size Delvoye envisions it in its final form. "There are more storeys in my computer," he says.

He hoped to install "Torre" on the roof of the Foundation's Palazzo Venier dei Leoni rather than at its canal-side entrance but was told that it would interfere with the city's skyline. Now, he says, everyone recognizes that he was right. Viewed from the Accademia Bridge, against the distant round dome of the Church of the Salute and the burnished orb crowning Pinault's Dogana, Delvoye's ambiguous, lacy structure looks a bit like a spiky, oversized lantern.

In the Arsenale Novissimo, Fabre is showing "From the Feet to the Brain", a massive, five-part installation. The work's separate sections (feet, sex, stomach, heart and brain) treat the artist's familiar themes: artist-as-warrior, as creative fount and as seeker of truth and beauty. The sex and brain components feature the artist's own effigy.

"I'm a provincial artist in a sense. I don't adapt to fashions or moods in the art world. I'm a one-man movement," Fabre tells me, with no false modesty. "My biggest inspirations are scientists. Curiosity is my biggest drive."

And so it is with Koen Vanmechelen, creator of the Cosmopolitan Chicken Research Project, a cross-breeding exercise that has now produced 10 generations of hybrid fowl. "Chickens are a race, like Homo sapiens," he says. "We create races in our heads. The culmination of my project will be when the genetic code of all chickens is shown to be the same." He's being assisted by the reputed geneticist Jean-Jacques Cassiman of the Catholic University of Leuven, who will trace the genetic code of all the artist's "works". At the Scuola Grande Confraternita di San Teodoro, Vanmechelen is showing hybrid sculptures of glass and steel, wood, feathers and hide.

"I also give conferences and lectures," Vanmechelen says. "Last year I spoke on diversity at the World Economic Forum. Barack Obama is the Cosmopolitan Chicken. For him, Africa is normal, Arabic countries are normal. Hybrid is the future, not pure race. Break your own cage."

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