Fig.: to do something superfluous and pointless

Sending her flowers for her birthday would be like carrying coals to Newcastle: she owns a flower shop

Regalarle fiori per il suo compleanno è come portare vasi a Samo: ha un negozio di fiori

Newcastle, in northern England, is in the heart of the main coal-mining region. Five centuries ago, its coal was already being shipped to London for heating; it would therefore be the last place one would need to bring coal to