The Princess Albertina is a female genital piercing. It is called a Princess Albertina, because, like a Prince Albert it passes through the urethra.
Due to the differences in anatomy, the piercing is totally unlike a Prince Albert. Whilst a Prince Albert passes through the head of the penis, the hole through which a Princess Albertina passes goes between the urethra and the vagina. The jewellery used within such a piercing is almost always a fairly small (about a 10 gauge) ring. Whilst a rare and complex piercing, a Princess Albertina is usually not very painful.
Supposedly such a piercing can be quite stimulating to the urethra, but the feeling may not be enjoyed by all women. After the piercing has healed it should not not interfere with normal sex. It is important to wait for the piercing to heal however, as urethral infection can lead to serious complications.
Disclaimer: Think long and hard before being pierced. Always seek out a reputable and experinced piercer.