Many of the older, non-glass backed courts, had no doors.  In order to get into the court there was a ladder, usually in the left hand rear corner, that was pivoted at the top and had a counter-weight.  To enter the court you pushed the ladder down and then, when the players were on court, you pushed the ladder up, and it stayed up because of the counter-weight.  A rope hung down to just above the rear wall so that you could pull the ladder down when you finished your match.  The rough diagram below will give you some idea.  Of course, there was always the prankster who marooned you on court by putting the rope out of reach.
This page, apart from being historical, may help court providers who are working to a strict budget or have no space immediately to the rear of the court at ground level.