Bartholin's duct opens into:
Bartholin’s glands are pea-sized oval glands in females homologous to Cowper’s Gland in male.Q bulbo urethral glands in males.
The ducts of Bartholin gland is 2cm longQ and opens into the vestibule outside the hymen at the junction of the anterior 2/3N1 and posterior 1/3Td in the groove between the hymen and labium minora.
A duct as well gland is lined by multilayered columnar epithehumQ (Not by transitional epithelium as is usually stated). 
Function of the gland is to produce abundant alkaline mucus during sexual excitement.
Labia majora and minora
A groove between labia minora and hymen
The lower vagina
The upper vagina