In Hollow Knight: Silksong, the Key of Apostate is one of the most important keys you’ll need to progress through the Slab. It’s hidden deep within the prison and only becomes available after collecting other keys along the way. This key not only unlocks some of the final doors in the Slab but also gives you access to shortcuts, escape routes, and valuable rewards. If you want to fully explore the area and reach new parts of the game, finding and using the Apostate Key is a must.
Key of Apostate Location

The Key of Apostate is tucked away deep inside the Slab, but you won’t be able to get it right away. First, you’ll need to pick up the Key of Indolent and the Key of Heretic. As you explore the cell blocks, keep unlocking doors you’ve already passed and make your way further down into the lowest levels of the prison. Eventually, you’ll reach the chamber past the Heretic trapdoor; this is where you’ll find the Apostate lock, along with the key made for it.
How to Use the Key of Apostate in Hollow Knight Silksong
Later in Hollow Knight: Silksong, you’ll come across a locked door in the Slab that can only be opened with an item tied to the Apostate. Head to the Slab Bellways to find one of the doors that needs the Key of Apostate. Starting from the Bench, go left and climb up to the level above.
From there, head right and jump onto the higher platform. You’ll spot a door with a keyhole next to it. Interacting with it will show that it requires the Apostate Key. This key also opens another locked door on the north side of the Slab. Go inside, complete the platforming challenge, and you’ll be rewarded with a Mask Shard waiting at the top.