In The Vampire Diaries, S01E11, Why does Damon takes Elena to a far off city and then to a bar?
What was his purpose? In an earlier episode it was said that he does everything with a purpose.
from Vampire Diaries wikia:
Damon came with Elena here(Bree's Bar in Atlanta, Georgia) in the episode Bloodlines to ask Bree for help. Damon, hoping to release Katherine from the tomb without the crystal, seeks out Bree's help.
Damon needed the help of a witch to know and to open the seal on the tomb of Katherine. Bree was a witch who was on friendly terms with Damon, and hence he went to her to ask for help.