Duke's Party was a party by the cemetery threw by Duke, a student who goes to Duke University and every time he returns to Mystic Falls he throws a party. In 2010, he was first seen. Jeremy invited Anna here.
She said she was leaving town and then they shared their first kiss. Then Ben McKittrick hit him to use him later on. During the party Grams and Bonnie opened the tomb. They just opened the tomb's door, they didn't removed the seal that keeps vampires for coming out. Damon entered with Elena, then Anna. Ben tried to fight Stefan, but was set aflame and died.
Grams told Stefan about the seal and he didn't enter, until he heard Elena screaming. Bonnie insisted to remove the seal, so that Stefan could get out. They did it, and after Damon realized that Katherine wasn't in the tomb he threw a pack of blood on the walls. Vampires in tomb drank that blood and left the tomb.
The spell weakened Grams and she died peacefully that night.