A BIG question mark hangs over the city of Liverpool. It glows acidic yellow. “What does it mean?” I ask a man on the banks of the Mersey.

“It’s an art work,” he tells me. “It’s meant to make you think.”

“Make you think about what?” “About Liverpool?” he guesses. Then he laughs. “About whether it’s a city or just a building site?”

Invest in a catalogue for the Liverpool Biennial (and you will definitely need it — few conceptual pieces are self-explanatory) and you will find that the question mark is supposed to make a slightly more probing point. But visitors will understand what the man by the Mersey meant. Liverpool, as it prepares for its 800th birthday celebrations next year, and its appointment as the European Capital of Culture in the year after that, presents a landscape of muddy craters and scaffolding, of cranes and traffic cones.

The city may be in flux but its biennial has become a fixture. This is the fourth, and the core components are established. The John Moores painting prize is held at the Walker. Abstract is out. The figurative and the photorealist are in. The winner’s hallucinatory homage to Vermeer is just one of several wacky landscapes with environmental implications.

Tate Liverpool hosts International 06. The gallery becomes a sort of conceptual playground incorporating anything from a box containing a knitted tortoise to what promises to be this year’s most controversial contribution. Teresa Margolles drips water, which has been used to wash corpses, on to a sizzling hotplate. As it evaporates spectators breathe in the vapours. International 06 artists — mostly established globetrotters — offer a chance to keep up. But Bloomberg’s New Contemporaries tries to race ahead. This year, the trend- setting show takes up residence in an experimental new arts complex in Greenland Street. It includes anything from wispy collages of paper clippings to hulking great sculptural installations. I particularly enjoyed the wit of the Rake’s Progress as retold through Yellow Pages and Katy Moran’s intriguing paintings, beautiful abstracts that looked more like Old Masters, like dark Dutch interiors or Fragonard confections.

But the real test for the art lover is: is that an art work or a civic artefact? Anything can be art from the funny smell on your hand (visit FACT) to those mysterious splashes in the basin of Albert Docks.

Don’t miss the imperial lions in their cages and the boats in the bombed-out church.

But there’s still one question mark. Why do so many conceptual pieces need such complicated screeds of explanation to support them? The city may be under construction, but art should not need a scaffolding too.

Opens today

www.biennial.com