Bartholin glands are located at the entrance of vagina on both sides. They cannot be seen with naked eyes when normal, but only visible if they are enlarged. They secret fluid in to the mucosal surface of the labia.
If it occurs due to infection it leads to Bartholin abscess. It is common in women who have never been pregnant. It can vary in size from size of pea to the size of an egg. Certain sexually transmitted disease like syphilis can cause these cyst.