Details 421 showed the man digging the hole for The Crucifixion of St Peter, early 1550s, one of Michelangelo's final two frescos, painted in the Capella Paolina in the Vatican. St Peter, by his own pious request, was crucified upside down (though he eyeballs the viewer crossly); the companion fresco shows another moment of apostolic bouleversement, The Conversion of St Paul. Both have strange, mobile viewpoints, half ground- level, half overhead. The chapel is in the Papal quarters, and you have to make a special appointment.

The first three correct entries came from: K F Lucas, Lincolnshire; D Binnie, Bromley; and H Thomas, Norfolk

In which painting by which painter can you find this gloom?

Answers on a postcard, to arrive by Monday 15 March: DETAILS 423, IoS, 1 Canada Square, Canary Wharf, London E14 5DL. Three winners will each receive a bottle of champagne