This is the pot puzzle some of you may have already stumbled across but not had the solution right away.
The secret garden is located up from the Estate of the Urn Witch Door. Keep heading up in the direction of the manor until you see 3 pots on your left, at this point destroy these and head left to reach a pot puzzle in which you have to destroy specific ones in order to open the tomb and reveal stairs to the garden.
It's hard in words to describe, but if you oriatate it the direction you came at it from:
X X X
X X
X X X
X X
X X X
The order would be as such:
3 1 X
X X
X 5 X
X 2
X X 4
It can be easier to use the bow as it can only hit 1 pot at a time, whereas if you started off with the sword attack, when going for the 2nd pot for example you may hit more than one. Just melee when going for the side ones where there's no risk of hitting any other.
Don't worry anyway as the pots reset if you mess up.I hope that gets it across to you if you prefer text guides.
Once open simply walk down the newly opened stairs and into the secret garden. There are two plant pots here for seeds as well as a collectable trowel. This trowel is great as it glows in your inventory in the post-game at night when there's a seed in the area. So this in combination with the red doors in post-game make mopping up significantly easier.
If you'd prefer a video, which in my opinion works better for this. Here is a 40 second video of the route to the puzzle from the Estate of the Urn Witch Door and the puzzle solution also (the stairs are already open for me)
Anyone that is interested where you find this solution in-game, there is an
Old Photograph collectable that is found in the
Ceramic Manor. From the Ceramic Manor Door go up the stairs and head right, go past the fireplace room and then when you come out, right next to the door will be those specific iron fire pit things. Shoot a fireball at this and on the right wall will open a secret ladder. Simply take your time crossing the beams and the photo is right next to the safe.