A "pink fortress" is a vagina, quite simple really.
Tyrone: "Yo I got let in Cindy's pink fortress last night!"
Jamal: "That's neat!"
To attack one's pink fortress is to have vaginal intercourse, or if you don't know, the act of shoving one's penis into her vagina
Past tense: Attacked her pink fortress
Tyrone: "Yo, what you doin' wit' Cindy, man?"
Leshawn: "Attacking her pink fortress"