Celts The misty world of druids, King Arthur and the Book of Kells is brought to life in an epic survey of ancient Britain and our ideas about it.
• At the British Museum, London, from 24 September until 31 January.
Other exhibitions this week
The World Goes Pop A global survey of pop art, less Campbell’s Soup and more manga than westerners usually imagine it.
• At Tate Modern, London, until 24 January.
Mat Collishaw Dark and sensual explorations of the psyche and society from one of the cleverest minds in contemporary British art.
• At New Art Gallery, Walsall, and Birmingham Public Library from 25 September until 10 January.
Prem Sahib Minimalist evocations of the body and the senses in Sahib’s first big London show.
• At the Institute of Contemporary Arts, London, from 24 September until 15 November.
Hannah Collins Emotionally powerful and historically atmospheric photographs by a substantial and serious artist.
• Baltic, Gateshead, from 25 September until 10 January.
Masterpiece of the week
The Gorgon’s Head Carved by Gaulish craftsmen for the pediment of a Roman temple at Bath’s hot natural spring, this face seems eerily Celtic and magical – the green man of the woods, the face of Merlin – although archaeologists currently suggest it may be the Roman god Oceanus. Alternatively, it is a snake-haired gorgon protecting the temple. Strange, spooky ancient stuff.
• At the Roman Baths, Bath.