This is an advanced sexual act, performed when one is feeling in the mood to surprise ones lady. You start this delight by turning off all lights in the room. Get your lady to lay on her side and ask her to look at the ceiling. Now, grab your erect meat seeking pissile and shine a torch from underneath to display the sillouette on the ceiling, while screaming "TO THE BATCAVE" and with one swift, vigorous thrust, insert ones member into her anus. Lube is optional, but dry docking is not recommended unless you do not value your teeth/balls/relationship.
I gave Tonya a real good batcaving last night. Luckily, she enjoyed it so didn't even knock my teeth out afterward.
Staying up late at night and into the early morning (usually in a confined space such as one's room or house) while sleeping for most of the day, much like a bat.