Hi,
I have a day plan to visit the Vatican city, Sistine Chapel, and the cathedral. Where can I buy the tickets?
There are no tickets required for the main part of the basilica. (It's not a cathedral since that's the seat of the bishop which is St John Lateran for Rome.) The line is for security screening and dress code check. Tickets for the cupola and treasury are sold inside.
Museum / Sistine Chapel tickets are sold at the entrance.
You are able to make reservations for a certain time however that will help you avoid the long ticket buying lines. On their website. Small fee is charged for the service but well worth it.
can I buy tickets online, so I can skip the lines?