Locked door. (Dark Souls 3)

ThurboCat
ThurboCat wrote:
there is a shortcut to the boss behind it.
It's right. It opens from the inside. Follow the long path to the boss and you will figure it out.

It is logical: somewhere near the arena there will be a transition to the boss.
The author himself answered this question.

did not notice this in Lothric, where is it at all? At the very beginning or will it be a location in the future?

James_Mails
This is right at the beginning of the location, you need to go from the fire to the right, and then immediately, ignoring the NPC, jump down.

ThurboCat
and, I blunt, it will open on the other side, first go through the other side, and there it will be possible to open it