Demon's Souls Secret Door: How to open
First off, you need to know where to find the secret door in Demon's Souls. It can be found in the Tower Knight Archstone area (1-3) behind some rubble and a fake wall.
You can check out the video in the Reddit post embedded below showcasing the exact location.
First up, you need to play the game in Fractured Mode. This mode reverses the placement of the world and adds a new item called the Ceramic Coin.
You then need to farm roughly 30 of these coins (some have reported needing less) and hand them all to Sparkly the Crow.
The NPC will then give you a Rusted Key, which you can use to unlock the secret door in Demon's Souls, and claim some great rewards in the process.
Demon's Souls secret door reward
For opening the secret door in Demon's Souls, developer Bluepoint has left a great Easter Egg reward.
For opening the door, you get the Penetrator armour set, which makes you look quite like the boss of the Tower Knight Archstone (1-3) world.
The Demon's Souls community have been asking Bluepoint to add this armour set to the game ever since Demon's Souls for PS5 was announced, so it is a great little treat.
Check out Distortion2's video below showcasing exactly how he opened the secret door in Demon's Souls, becoming the first recorded player to do so.