A while ago i was quite into all that Dark Souls mistery stuff, most of all the pendant, the statues ant the furtive pygmy.
I came across a 3D-Mapviewer at some time and spent hours analysing the structures of the levls. When i was looking at the shortcut to Lost Izalith i could clearly see thet there had too be a secret door.
To be more precise it should be down the roots from the Demon Ruines side, again down the stair and there to your right about half way to the gate. If you look pretty close you can even see that there is a litte dark arc which you can see within the red stone.
I was really sure that this had to be a secret door which somehow could be opened. So i tried alot of spells and equippmentcombination but i n ever managed to open it. But this wasn't all for nothing. Once the Miracle "Force" hit the wall you could see, what i called, a hitanimation. These animations only occured where the door i was searching for should be or the Miracle hit an enemy.
But after that i went out and tried this spell actually everywhere the 3D-Mapviewer didn't show something which was actually there in the world. First i started with the other secret door and saw that whilst they were closed they showed the hitanimation. The statues in Undead Parish and The Catacombs (woman with crown, baby and sword), the statue at the Firelink Shrine,the Statue down in Anor Londo in front of Gwindolin, befor it dissappears becauso of the ring, showed these animations too. Adding the Statues to your left and right in the corridor to The Duke's Archive, the door in Upper Undead Burg with the wooden crates down the stairs to the "first" Black Knight and the culloms inside the church at Undead Parish.
The culloms showed me something important which was that i couldn't destroy them but the Tower Knight which spawns there once by default (i had him spwan twice while i was waiting for Petrus to kill Reah... offtopic nvm) had no problems destroying them. They would respawn, once you went through a loading screen i suggest. After that i tried to get crazy Solairis to kick open the door down in Lost Izalith but he wouldn't go through the gate. The last thing i tried was to start a new playthrough an try to get the Dark Knight in Upper Undead Burg to smash against the mentioned door. But i dind't finish this.I wanted to wait some years for all the secrets to be revealed.
To sum this way to long and maybe unclean written post:
Special Objects show a reaction to the Miracle: Force
-Secret doors befor opening + door in Upper Undead Burg
-Satatues (Firelink Shrine, Undead Parish, Catacombs, The Duke's Archives)
These Objects sometimes can't be "destroyed" by the player but by NPCs (culloms Undead Parish)
Lets see if someone else manage to get something out of this information and have fun. In my opinion the secret door in Lost Izalith holds the "Old Witches Ring" but we'll see if this is true once it's open.
P.S. not sure but i think the hidden paths in the Crystal Caves showed the same reactin to Force.