Ciao a tutt*. I see this thread focussed more on the second phrase 'cose di un altro mondo' but I feel that 'cose mai viste' has a slightly different meaning - I translated it as 'unprecedented'. The context is a comment by Indro Montanelli about the Rome 1960 Olympics:
La Svizzera, che doveva ospitarle, le Olimpiadi le ha declinate. Ha detto che il suo bilancio non le consentiva di spendere miliardi su miliardi in attrezzature di cui poi non avrebbe saputo cosa farsi. Roma ha brigato per farsele assegnare. E non esito a credere agli organizzatori, quando dicono che faranno « cose mai viste », in tutto « degne del grande nome e del prestigio dell' Urbe (Corriere della Sera, Sunday 30 August 1959, 3.)
Switzerland, who were going to host the Olympics, declined. They said their budget did not allow them to spend billions upon billions on infrastructure that they would not now what to do with afterwards. Rome schemed to have them assigned. And I don’t hesitate to believe the organisers when they say they will do "unprecedented things", that will be overall “worthy": of the great name and prestige of the Eternal City
Let me know what you think (also a bit hard to tranlsate 'l'Urbe' which is why I went for the more popularly known synonym Eternal city but that is probably a thread in itself)
Flavia