Beyond the bridge in Tate Modern's Turbine Hall stands a huge steel chamber, raised above the floor on steel legs. You can wander among the supports. This is unnerving. Your walk is curtailed by the underside of a ramp that leads into the open end of Miroslaw Balka's How It Is, the 10th Unilever Turbine Hall commission. The interior appears as a black, open void, facing the end wall of the Turbine Hall and swallowing the light. At first, you can't see into the depths. Even perspective seems distorted; there's no discernible vanishing point. If the walls close in, so the dark seems to open out, both unfolding and enveloping. You wrestle for a sense of volume, and end up feeling the walls for guidance. They are lined, unexpectedly, with felt.  Balka has also covered some of the Turbine Hall's skylights, reducing the overall light level, and the looming darkness inside the steel structure feels both palpable and impenetrable. There is nothing here except the contained dark, which itself seems to have mass and density, weight and substance. The title invokes the dark and mud of Samuel Beckett's 1961 prose work How It Is, all the endless crawling, yard after yard, towards nothing at all. One searches for limits, as if they might offer some kind of comfort. Instead, the containment makes you feel even more puny. It is a space whose limits are sheer walls instead of a horizon, with more blackness overhead. It is a darkness you struggle to measure, or rather a darkness that measures you.  Slowly, your eyes adjust to the light leaking in, the slight reflectivity of the steel floor, the thin light brushing the felt-covered walls. You expect echoes, but there aren't any. Hell is the people in here with you. An absolute simplicity stops it being another of art's tunnels of love or mystery trains, although one wonders what kinds of games people will play here.  Even so, it is a space that asks for silence. Recently I spent time with the artist in his native Poland. We visited Treblinka together at dusk. Our conversation there drifted into silence and the darkness of the surrounding woods. Balka often invokes history, terrible events, human suffering and the plight of the body. Some of his sculptures use human hair, ash and soap; others allude to the burial pits and death rooms of the Holocaust. But he insists that these are not his subject. Instead, he says, his art is about being human.  One approaches this with both trepidation and scepticism. Many artists pay lip service to big issues. But at its best there is something irreducible about what Balka does. There's also a limit to what can be said. How It Is might be a box in which we can place all our miseries, a cinema without a movie, open to all our projections. The most powerful image is watching people stand at the top of the ramp, hesitating on the verge of the consuming dark. But Balka reveals darkness rather than cloaking it in mystery. That is the point, and why this work is so successful.  How It Is joins Juan Muñoz's 2001 Double Bind, Doris Salcedo's Shibboleth and Bruce Nauman's sea of voices, Raw Materials, as the most successful of the Turbine Hall commissions. They are the best because they return you to your own resources as a spectator: they seek less to entertain than to give you pause. All are invitations to the imagination, returning us to our own thoughts.
Adrian Searle: Filled with nothing but blackness, this cavernous installation at Tate Modern leaves us teetering on the brink