Unfortunately, would-be-enterers were quite rare and would-be-exiters even more so. The sphinx flipped through a book of riddles left to her by a visitor some years ago. She was particularly fond of the puzzling question of “what has four wheels and flies?” but thought it lacked the requisite gravitas for interdimensional travel.
She also didn't quite understand the answer.
So, when the next traveler came across the lonely sphinx, the ancient greeting changed. “Answer me these riddles twenty-three.”