The Stonesword Keys in Elden Ring are used to unlock certain types of doors scattered throughout the world. Check out this Elden Ring Stonesword Key location guide to find them all as you play the game. This way you can get through those pesky fog doors blocking your path.
Elden Ring Stonesword Key Location Guide
First you will want to get to the Rampart Tower bonfire. From there go out into the hall and take the wooden steps up. Run outside and kill all the enemies before going up onto the wooden platform. Look east on your compass and jump onto the stone ledge there. This will give you access to the roofs below.
Follow the stone ledge around to the right and wrap around until you can jump across a gap to another ledge. Do that and drop down inside the tower to find the key.
Lots of Merchants selling the keys as well.