"Help me find it." Harry said to Moaning Myrtle, "If my guess is correct, the entrance to Slytherin's chamber must have a snake emblem... you look for it too."
"How do you know?" Moaning Myrtle asked quite interestedly; she was more curious about how Harry knew this than about finding the snake mark.
"Because I have been to Slytherin's study room before." Harry said slowly, "Outside Slytherin's study, there were always many small snake-like marks. If you speak Parseltongue to the snake, it triggers a mechanism that opens a hidden door."
"Is there such an interesting place?" Moaning Myrtle was even more curious, "Then, Mr. Potter—no, Harry, can you demonstrate what Parseltongue is to me?"
"I can't actively speak Parseltongue, Myrtle." Harry glanced at the still excited Moaning Myrtle, "I can only passively trigger this ability when I see a snake—if you can find the thing, I can demonstrate it for you."
Upon hearing Harry's words, Moaning Myrtle immediately turned around to help Harry look for the small snake emblem in the pool.
The two of them checked the pool inside and out, top and bottom, without even missing the pipes below.
"Hey, here." Moaning Myrtle pointed to the side of a bronze faucet, "I remember this faucet, it never runs water no matter how much I turn it... it seems this must be the small snake emblem you mentioned—well, now that I've found it for you, you should demonstrate Parseltongue."
"Seems you've mistaken me for a member of a circus." Harry said helplessly.
He leaned in closer, looking at the small snake.
Actually, his talent in Parseltongue was not obvious, but after special training from Omnius, he grasped part of it.
"Open." He hissed, as if speaking with a slurping tongue.
Upon hearing the hiss of Parseltongue, Moaning Myrtle showed a look of delight.
"I just knew it!" she said excitedly, "I remember it now! The boy I mentioned also spoke Parseltongue!"
As soon as she finished speaking, the faucet with the small snake emblem emitted a dazzling white light and began to spin rapidly.
Following that, the pool also began to move. They watched as the pool slowly disappeared from view, revealing a very large pipe large enough for a person to squeeze through.
"Is this the entrance to the Secret Chamber?" Moaning Myrtle asked in shock, "I've been here for decades and never knew that a secret passage to the Secret Chamber was hidden in the girls' bathroom on the second floor..."
"Yes, this is the entrance to the Secret Chamber." Harry said concisely, "Alright, Myrtle, thank you very much for your help, but I also ask you to keep this temporarily secret until Dumbledore can catch the boy who killed you at the time, okay?"
"Don't worry, Harry, I promise I won't tell anyone!" Moaning Myrtle said, patting her chest.
"Also," Harry took a few steps, noticing that Moaning Myrtle followed him, then added, "you should wait here, please, definitely don't follow me down."
"What, are you worried I'll die again?" Moaning Myrtle laughed, "Don't worry, Harry, I'm already a ghost, I can't die a second time."
"But according to the books, a ghost will turn to stone if it looks into the eyes of the Serpent Monster." Harry said helplessly, "If you don't want to be the first ghost to be petrified, I suggest you wait here."
"Alright then." Moaning Myrtle spun around and said, "I'll wait here for you."
Harry stood in front of the pipe, took a deep breath, propped himself at the mouth of the pipe, placed an Armor Protection under his butt, and then slid down the length of the pipe.
The feeling was not pleasant, kind of like being on a water slide in an amusement park—Harry once remembered being taken on a water slide by his cousin Dudley, and the feeling was... not very good.
This pipe did not run straight down; instead, it twisted and turned. Harry felt himself bumping against the sides of the pipe, making light thumping noises, and if not for the Armor Protection under him, he would have likely sparked a fire.
Luckily, the feeling didn't last long; after about five minutes, Harry finally felt an expanse before him. He popped out of the pipe opening.
"Arresto Momento!"
Harry pointed to the ground and cast a cushioning spell to stop his fall, avoiding a collision.
While not seriously hurt, being bumped was indeed painful.
"Revelio!"
The spell didn't detect any creatures.
"Lumos!"
He raised his magic wand, the tip illuminating enough to light up around him.
Here... seems to be the bottom of the Black Lake?
Harry looked around and found himself in a stone-built tunnel. The surrounding walls were dark, sticky, and seemed to be covered with a thick layer of moss—or maybe some grime.
The tunnel was silent, and Harry could even hear his breath, clearly.
He tried to walk forward, and after a few steps, he heard a crunching sound underfoot.
He had stepped on a rat's skull.
Walking a few more steps forward, Harry saw the remains of a snake shedding on the path ahead.
The light from the magic wand shone on the snake skin, making it emerald and looking very vivid.
Without saying anything, he stuffed the snake shedding into his wallet.