Hello, I will arrive in Rome the week of June 20th. My husband and I are fully vaccinated . We have a tour planned to visit Venice, on way of a high speed train. Are there any COVID restrictions for the train ride to Venice? What is the green certificate, and is this a requirement to visit Venice and board the train? If someone can answer my questions I would greatly appreciate your help. Thank you in advance , Connie Stonecipher, from Houston, Texas.