batcave entrance 

A vehicle entrance to a facility that is obscure and infrequently used. Often the only people who know of this entrance are the employees who work there. Golf courses, farms, industrial parks, sports facilities and outdoor museums often have batcave entrances. Management often frowns on use of this entrance. This term is inspired by the "Batman" TV series from the 1960's. In that program, the entrance to the Batcave was down a little-used dirt road that was blocked at one end by a fake wooden barrier.

My boss told me I had better not be late again, so I had to use the batcave entrance to get to the office on time.

batcave entrance by Led Zeppole October 30, 2003