This question got me to wonder why Hogwarts ghosts never knew about the Chamber of Secrets.
Some ghosts have been around Hogwarts for centuries. Plenty of time to explore the school grounds, talk to people who might know, or talk to the person killed by the basilisk. "So the last thing you saw was a big pair of glowing yellow eyes over there by the sink? Well, Nick, let's float down through the floor by the sink and see what's there."
They can move through walls, so they can access the Chamber of Secrets without needing to say "Open" in a Parseltongue.
They are immune to or less affected by hexes and charms that would bedevil living residents.
They had many opportunities over the centuries and the means to do it. Why didn't the ghosts discover the Chamber of Secrets?
Please support your answers with quotes from canon sources.