Describing the Venice Biennale, like pinning down the city itself, is a practical impossibility. There is just too much of it, tucked away, scattered throughout the maze of alleyways and canals. And the art is no longer confined to the Biennale’s national pavilions in the gardens. It has spread, via dozens of tagalong shows cashing in on the presence of the global art world, to a motley array of disused palaces, warehouses, churches, at least one shop and a hidden garden loggia.