Cairns, the ancient Celtic way of stacking rocks, has long found a new-age audience amongst stressed out city slickers and overworked tech execs trying to tether themselves from their screens. Balancing stones requires poise and concentration. The practice is often used as a new form of mediation; in Korea stones are stacked as a form of prayer. Long fascinated with nature’s pull onto humanity, the Swiss artist Ugo Rondinone’s new mountain sculptures come via his erudite preoccupation with German Romanticism. Rondinone’s precarious, gravity defying totemic assemblages are hardly the stuff of nature, though. They are hand-formed clay, cast in aluminium and painted in shocking day-glo colors; their placement on plinths clearly marking them as artworks more at home on the gallery stage rather than on a pine-cushioned forest floor. At Gladstone Gallery through October 22.