Either defeat or evade this phantom and jump into the faded fog in the hole to complete this stage. This portal can only be accessed by defeating the Giants and acquiring the Forgotten Key. There are four black phantoms and two white spirits to defeat.
Continue going left to light the Chasm torch and then follow the path to the exit.
On the way out, there is a black phantom dual-wielding a shotel and a flamberge.
The Dark Chasm of Old is an optional area in Dark Souls 2.
The Chasm is accessible only to member of the Pilgrims of the Dark Covenant.
Go further, and you can activate the Priestess' Chamber bonfire. Take the platform down and jump to the side as it lowers down. Further around you'll find a chest with the hex Dark Greatsword.
Use the Aged Feather to go back to the bonfire you activated.
This portal can be accessed by going to the Shaded Ruins in the Shaded Woods.
Head toward the path leading to the boss and walk toward the tall grass.
The second portal can be found at Drangleic Castle near the first bonfire.
As you enter the room with the two golem statues holding the torches, go to the furthest room on the left, dodge the Ruin Sentinel and drop into the hole.
This will lead to a hidden cave with a bonfire (Under Castle Drangleic).