This is a dedicated boss area with almost no exploration required. This is accessed by crossing the second stone bridge in Huntsman Copse and following the path until you cross the long, wooden bridge leading to this area.
Boss: Executioner's Chariot
The boss will be encircling around the area, destroying everything along its path. You have to keep your ears and eyes open to know when the chariot will arrive. The only way to avoid getting damaged is by hiding in the alcoves. However, the skeletons will pose a problem. Destroy the ones that pose immediate threat to you and find the necromancer. Kill it to stop the skeletons from respawning. There are two necromancers here; one is found in one alcove to the left from your starting position while the other is located to the right, near the lever. Take your time; the skeletons doesn't regenerate immediately. After taking out the second necromancer, make sure that no skeletons are roaming around.
Once clear, approach the lever and pull it to lower the gate. When the chariot crashes to the gate, the executioner will be killed and you'll have to fight the two-headed horse. It will charge and stomp, which you can easily anticipate. It also leaves itself open when its spewing dark mist. Ranged characters will be able to use this chance to pummel it with attacks. Melee characters can land a hit or two right after evading its attacks since it also has a bit slow recovery time.
After defeating the boss, you can now explore the area and loot the bodies. You can get Fading Soul x4 from the corpses littered along the path and a Soul of a Brave Warrior from the corpse hanging on the edge of the hole past the gate.
Enter the doorway and continue upstairs to find a bonfire and an NPC that will allow you to join the Covenant of Blood if you have a Token of Spite. This is acquired by killing another player when you invade their world. You can also find one from a chest at the bottom of the Grave of Saints.
If you join the covenant, you'll get a Crest of Blood. He will also sell a Great Scythe, Priest Chime, Bone King armor set, Delicate String, Hexing Urn, Silver Talisman, Red Sign Soapstone and pyromancies like Firestorm, Great Combustion, and Fire Whip.