In the Elden Ring location of Stormveil Castle, there is a locked door a short distance southeast of the Rampart Tower Site of Grace. The door is on a balcony overlooking the east end of a large room with many meathooks hanging from its ceiling. The room is patrolled by a large, dangerous Grafted Scion. When you try to open the door, you will receive a message telling you that it does not open from this side. Here’s how to get to the other side of the Rampart Tower locked door.
Starting on the locked side, go back along the balcony and turn right. You can either fight the knight in here, or you can run through to the doorway in the far corner (go across the raised platform to make it harder for the knight to get you). When you exit the room, immediately turn left and jump over the wall where the sandbags are.
Turn left again and stealth kill the guard, then go up the steps and then along the wooden platform. Go up the ladder at the end of the platform, then go straight ahead and drop off the end. Kill the guard, then turn around and open the door to the south. You have now unlocked the Rampart Tower door.