Helsinki Art Museum (HAM)

This guide to the Helsinki Art Museum takes you into the old Tennispalatsi, an Olympic tennis hall built in 1938, to trace how deputy mayor Erik von Frenckell commissioned a young Tove Jansson to paint two frescoes for a city hall canteen in 1947, with one strange condition: hide a Moomin among the flowers. She spent six months painting straight onto wet plaster, taught by a fresco specialist, with her own sculptor father lending a hand. Look for the vaulted gallery where those frescoes now hang.