A classic gift for Grandma is a bottle of eau de cologne, invented in, yes, Cologne in the late 18th century. The most famous is 4711, named after the address where it was first created. The building now houses a flagship store and a museum where you can marvel at a giant Gobelin tapestry and stop by the Fragrance Fountain.
Note the carillon outside with characters from Prussian lore parading hourly from 9am to 9pm.
If you're really into colognes, enquire about tours, creating your own scent at a seminar and indulging in a 'fragrance menu'.