Speaking with this NPC will grant the player access to Ariandel automatically.
If you aren't familiar with the bonfire by name, it is found in the building which serves as the central 'shortcut hub' of the Cathedral of the Deep - you know, the fancy church with golden double doors and tons of smashable wooden chairs inside. He can be found kneeling to the right of the nearby altar. PDT for console users, Ashes of Ariandel will be accessible with the help of a new NPC who appears very close to the Cleansing Chapel bonfire. Thanks to these folks, the rest of us have been spared hours of frustration and aimless searching.
Fortunately for Dark Souls fans, the unexpected early release of Ashes of Ariandel for Xbox One last week allowed a few brave pioneers to find the gateway to Ariandel ahead of the rest of us.