You can teleport to the outskirts of its' lair using the boss teleport to 'King Black Dragon.' Afterward, enter the gate east, and climb down the stairs. Proceed to head north and you will run into the almighty KBD (King Black Dragon).
This beasts' fire hits extremely high if you aren't careful, so make sure to wear an Anti-Dragon Shield , or a Dragonfire Shield to take some of the hit for you. Plenty of food is highly reccomended, as well as potions. A team of High-leveled players is also highly recommended.