Ghostly Encounter

When I was in college, I was working on the soundtrack for Equus up in the catwalk above the stage, late into the evening.
A theatre major, I usually was stage manager for productions, but for this show I was the sound designer.  Lots of weird music when the horses were on stage during this psychological drama.  Weisiger Theatre, located in the Norton Center of the Arts, was built in the 1970's, and legend had it that when the building was being constructed, a man was killed in the elevator shaft.
Alone in the theatre, late in the night, concentrating on splicing reel-to-reel tape, I heard the door to the catwalk open.  I looked up, and there was the silhouette of a person standing in the doorway.  I called out to the figure, and received no answer.  The figure was dark, but had a transparent quality to it.  I could see the hallway outside the catwalk through it.
The door clicked shut, and the figure was gone.
Like it had just disappeared.
I went to the door and checked it - it was locked from the inside, someone would need a key to open the door.  A security guard would have had a key, but they would have also answered the call from a student late at night.
I went out into the empty hall, and looked at the elevator.  It was still at that floor.  I hit the button, and it opened, no one inside.  I went into the stairwell, and it was empty, only my voice echoing as I called, "Is anyone there?"
The more I thought about what I saw, I realized it was a ghost.  There could be no other explanation.
I was more intrigued than scared.  I've had other spooky experiences in my life, but this is the one that, for me, is my encounter with a ghost.
How about you - have you had a ghostly encounter?