Arrayed in a semicircle, Manfred Kielnhofer’s ghostly “time guardians” seem to have abandoned themselves to infinite sadness. What do the life-sized polyester figures represent? Are they bereaved women, meditating monks or nuns or premonitory spirits sent to warn us of impending dangers? Are they supposed to inspire awe, compassion or fear? The artist refuses to tell us why he created them and if we dare to peer inside their cloaks we discover only black emptiness.