Simplify the following text for a Grade 8 native English-speaking person.
Original: The Seoul Metropolitan Government established several organizations to oversee the successful restoration of Cheonggyecheon : The Cheonggyecheon Restoration Project Headquarters for the control of the whole project , Citizen 's Committee for Cheonggyecheon Restoration Project for the management of conflict between Seoul Metropolitan Government and the union of merchants , and Cheonggyecheon Restoration Research Corps for the establishment and review of the restoration plan .
Simplified: The restoration of Cheonggyecheon took three years spending almost $ 400 million . Since its opening in 2005 , hundreds of thousands of people have visited Cheonggyecheon with friends and family .