The Czech capital, Prague, has been rocked by scandal. Serious mistakes were made during the refurbishment of the city’s world-famous Charles Bridge. Even UNESCO is asking questions.The Charles Bridge has been under renovation for three years now. Early on, citizen's groups protested against shoddy workmanship. Now they're receiving support from the government office for the preservation of historic monuments. It says the construction company hired to carry out the work has destroyed numerous historical stone blocks and replaced them with replicas. In addition it's alleged that the wrong kind of mortar has been used. The city of Prague is now facing a high fine. And UNESCO — which has once before threatened to strike the city off its list of World Heritage Sites -- has expressed concern.