One props up one's girlfriend onto her head. The recipient is now doing a head stand. The perpetrator of the rum cave holds the recipient's legs spread wide and pours into her muff a blend of several flavors of rum. The woman's legs are then brought close together again and she is spun around (for proper mixing of the rum in her muff). The rum cave girl is then bent forward so that one can drink the rum from her now sterile snatch. Add cut fruit pieces and a little umbrella for a tropical drink.
Mark invited Cris into his house and made a rum cave from which he happily drank throughout the evening.
When a guy pees inside a girl. He might or might not proceed to then lick/suck it off, this is called "Sobering Up the Cave".
Guy 1: I gave Tegan a Rum Cave last night and she loved it.
Guy 2: Did you sober up the cave?
Guy 1: Well, I was thirsty!