The quest to silence the Nightsong is not just a random task but an integral part of the Silent Library puzzle. It serves as a pivotal moment in the game, especially if you're following the Shadowheart questline. Successfully completing this quest not only progresses the storyline but also provides you with valuable rewards that can significantly aid you in your journey.
What Can Silence The Nightsong?
The core of this quest revolves around solving a riddle: "What can silence the Nightsong?" This riddle is the key to unlocking a secret chamber filled with treasures and progressing further in the game.
To solve the Nightsong riddle in Baldur's Gate 3, head to the Silent Library and beat the justiciar duelists. Use a lockpick to open the grate, and find the book "Teachings of Loss: The Nightsinger" on the second bookcase to your right as you enter. Place this book on a pedestal at the back of the room to reveal a secret chamber containing the Spear of Night.
Step 1: Reach the Silent Library

To get to the Silent Library, you'll first need to navigate through the Gauntlet of Shar. This is a sprawling underground chamber filled with various trials and enemies. You'll likely encounter creatures like justiciar duelists and other foes that serve Shar, the goddess of darkness.
Once you've made it through the initial challenges of the Gauntlet of Shar, you'll come across the entrance to the Silent Library. It's a large, ominous door that serves as the gateway to the puzzle you're trying to solve.
After defeating the guards, proceed to open the door to the Silent Library. As you step inside, you'll notice bookshelves filled with ancient texts and a mysterious atmosphere. This is where the real challenge begins.
Step 2: Unlock the Gate

Once you're inside the Silent Library, your next task is to find the large gate located at the far end of the room. This gate is usually made of heavy metal or stone and is often adorned with symbols or inscriptions related to Shar, the goddess of darkness.
If you have a rogue or a character with high dexterity and proficiency in thieves' tools, now is the time to use them. Astarian is a good choice for this task due to his lockpicking skill. Make sure you have a lockpick or thieves' tools in your inventory. If you don't have one, you might be able to find one in the library or earlier in the Gauntlet of Shar.
To unlock the gate, select the character with the lockpick and click on the gate. A skill check will usually occur, requiring you to roll a dice. If you succeed, the gate will unlock, granting you access to the altar and the next part of the puzzle.
Step 3: Find the Book

After you get through the gate, you'll see lots of bookshelves around you. You're looking for a special book called "Teachings of Loss: The Nightsinger."
This book is the key to solving the riddle. To find it, head to the right side of the room from where you entered. You'll see bookshelves lining the wall. The book you need is on one of these bookshelves, specifically on the southeastern side of the Silent Library.
Once you find the "Teachings of Loss: The Nightsinger" book, take it off the shelf and put it in your bag. You don't even have to read it; just having it is enough. After you grab the book, get ready to head back to the altar.
Step 4: Place the Book on the Altar

Now that you have the "Teachings of Loss: The Nightsinger" book in your bag, it's time to go back to the altar. The altar is at the far end of the Silent Library, behind the gate you unlocked earlier. It's usually a big, fancy table with some symbols or writings on it.
When you get to the altar, you'll see a special slot or space where you can place the book. Take the book out of your bag and put it in that slot. This is the key part of solving the riddle, so make sure you place the book correctly.
After you place the book on the altar, you'll hear a sound or see some lights. A door will open somewhere in the room, usually on the other side of a cage or barrier. Behind this door, you'll find some awesome treasures like the Spear of Night.
Conclusion
By solving this riddle, you'll gain access to powerful items like the Spear of Night and Dark Justiciar armor sets. These items are not only valuable in combat but also have lore significance. Failing to solve the riddle could mean missing out on these crucial items, making your journey through Baldur's Gate 3 more challenging.