So tell us the big joke, then

The enigmatic works of the great Spanish sculptor and showman Juan Muñoz amuse and unsettle in a welcome retrospective

Juan Muñoz: A Retrospective
Tate Modern, London SE1; 24 January until 27 April

Spanish artist Juan Muñoz died suddenly of a heart attack on a hot August day in 2001. He was 48 and at the height of his powers. The obituaries rang with incredulity that such a vivid spirit could possibly be gone, but the shock was also unexpectedly real for anyone visiting Tate Modern that summer.

Muñoz had transformed the Turbine Hall as no other artist before or since into a parallel world secreted between two floors. At the bottom of the building, in a Stygian gloom pierced only by shadows falling from tenement wells above, a secret service of grey-suited figures performed an enigmatic drama in a network of balconies and corridors: an unforgettable embodiment of purgatory.

But as you rose higher up Tate Modern, all trace of what you had seen mysteriously disappeared. Lifts descended but brought nobody back. Shafts in the floor turned out to be trompe l'oeil images, leading nowhere. The experience was somewhere between Magritte, Piranesi, Dante and Fritz Lang, except that you moved through it in three dimensions. Double Bind, as it was called, was an astonishing experience for the mind and eye. How impossible that it should be the sculptor's last work.

Juan Muñoz set out to astonish. His art is more like showbusiness - silent film, illusion, vaudeville, mime - than conventional sculpture. His best-known works involve nearly lifesize figures in dramatic monologues or groupings, performers who inspire bewilderment, laughter or, more usually, disquiet in the audience. For we seem to constitute something more than mere viewers for these characters, as he called them, to co-exist with or even for them.

Take Many Times, one of the signature works in the posthumous retrospective that begins its European tour, appropriately, at Tate Modern next week. In the central gallery, you will encounter a great throng of figures, a hundred apparently identical Chinese men, all bald, all grinning, in hugger-mugger confabs. As soon as you appear among them, you will simultaneously feel excluded, left out of the party or the secret or whatever the private joke may be. Yet with their unreadable expressions - surely they can't all be laughing at the same thing? - they seem equally alien to us.

Part of the grim comedy is precisely that they all look the same: an optical illusion of European perceptions. 'For Western people,' Muñoz said, 'it seemed to me that Chinese people are like a visual trick. I would make the noses shorter, the eyes larger, but still they all look like the same guy.'

He, or his cousin, appears seven times in Towards the Corner, a much-travelled work you might have seen in museums elsewhere. Here, the figures are assembled on wooden bleachers, laughing heartily at some event in the corner. Entering from behind them, you are irresistibly drawn to discover what's so funny, but, in so doing, position yourself as the butt of the joke. The defensive thought occurs that if you weren't there, they would still be laughing, wouldn't they, but laughing at what - their own collective absurdity?

The Spaniard is one of art's great late-starters. He only came to sculpture at the end of his twenties, having run away from Madrid to London at the age of 17 and experimented with all sorts of other art forms first. The earliest works from the 1980s are elegantly absurdist. Architectural fragments blossoming out of dead walls: banisters that wiggle as if one were sashaying down non-existent stairs; hotel signs above wrought-iron balconies that lead nowhere. They turn you into an actor, too, as you look up and inevitably imagine looking down, catching yourself as a passer-by on some Spanish plaza.

The suspension that is a balcony - neither in nor out, neither here nor exactly there - is an apt emblem for what followed. Muñoz began to make figures imprisoned by their in-between states: stringless marionettes, ventriloquists' dummies waiting alertly for a ventriloquist to give them words, a stage prompt poised in his box before a bare stage.

In Stuttering Piece, two seated figures are stymied by the never-ending dialogue repeated on loop between them:

'What did you say?'

'I didn't say anything.'

'You never say anything.'

'No. But you keep coming back to it.'

Beckett and Borges, TS Eliot and David Mamet: Muñoz was the most literary of sculptors. The dummy waiting to come alive is stranded on a shelf on the other side of an optical illusion of a floor so convulsive it looks impossible to cross - a wasteland leading to silence. Another trademark figure is mired from the waist down in a sphere like a large, grey Weeble. Helpless, tragi-comic, a little foolish, he or she must endure this sticking point forever, like Winnie buried up to her bosom in Beckett's Happy Days

The greyness of the figures is crucial - they must be as naturalistic as us, yet unrealistic enough to be Other. Muñoz hit upon grey after experimenting with other colours and one sees why it succeeds by comparison. A white female dwarf looks too much like a plaster body cast (which, in fact, she was); a terracotta dwarf looks too much like traditional sculpture.

This Dwarf With a Box (1988) stands in his suit upon a desk that brings him roughly to our level. But his eyes are closed, breaking the connection and repudiating the supposed advantage of height. You are thwarted, given the cold shoulder if you like. It is an inarticulate reproof that leaves one stuck for words.

Muñoz was never afraid of courting narrative even as he blocked it. You could make something of the chess box beneath the dwarf's arm, or the row blowing up in Conversation Piece, or the man with his face pressed so hard against the mirror you sense a horrible revelation dawning like that of Narcissus in reverse.

But even though his art veers in the direction of speech, of drama and dialogue, prologue and climax, at its best it conveys illusions, sensations or emotions that can't easily be put into words. Wax Drum is exactly as it sounds - a mute instrument, lacking the necessary skin. But plunged into it is a pair of scissors that somehow represents in one devastating gesture the whole of its defencelessly deafened state.

And high above the concourse at Tate Modern, already in place, two grey men are suspended in mirth. Out of the mouth of one of them trips a line of tiny iron figures in gesturing poses that cannot themselves be read. The joke is private; you're not in on the anecdote and yet the piece inspires corresponding laughter in the viewer. And perhaps that is Muñoz's grave point: laughter, like sorrow, exists beyond words and long before speech.

Three to see:

Roman Signer
Fruitmarket Gallery, Edinburgh, until 27 January

Last chance to see Swiss master of the absurd: miniature tragicomic videos.

The First Emperor British Museum
London, until 6 April

No two alike: China's famous terracotta warriors in unprecedented Western display.

Bauhaus 1919-1933
Middlesbrough Institute of Modern Art, until 17 February

Great artists or dictatorial designers? Depends on your taste. Including Gropius, Klee and Kandinsky.