Dragon key pieces are items which can be found throughout the Dragon Slayer II quest.
After speaking with Brundt the Chieftain to gain access to Torfinn's boat, players can sail to the island of Ungael where the dragon Vorkath resides. After defeating Vorkath, players are given access to the ancient laboratory beneath the island where the key will be found.
In this laboratory, several old notes can be found by searching the ancient equipment, a door can be found to the east, as well as a lever to the south-west. Once pulled, there's a limited amount of time that the doors stays open so players must be quick in order to enter the room. In this room, they will find an ancient key as well as the dragon key piece.
First speaking with Amelia in the Shayzien House revealing this piece is in the Shayzien Crypt. Filled with high level undead, it's suggested to use Protect from Magic with high Melee Defence and high Ranged Defence. With a light source, run through the crypt down ladders and staircases until a pair of doors are reached to the south. A riddle must be solved in order to obtain the key piece.
Speak to Reldo in Varrock. Search the bookcases for a red book then talk to Reldo again. Travel to Port Phasmatys and speak with a ghost named Sarah with a ghostspeak amulet equipped, just west of the bank. The key piece is lost and needs to be located. Speak with Ava in Draynor Manor. Use a dragonstone on two pieces of molten glass with a glassblowing pipe in your inventory. You will receive an Inert locator orb. Speak with Ava again and receive a locator orb. Use the locator orb within Morytania until you find the exact spot, and then, dig it up with a spade. It will damage the player upon use, so it is advised to bring food; however, it cannot actually do any damage past 1 health so the main worry within the swamp is ghasts.
You'll have to navigate the maze, with traps consisting of spike and man traps. The spikes can be disabled through Thieving, and man traps leaped over with Agility. To make matters worse, there are also multiple Stone guardians wandering the area in a multi-combat environment. Each Stone guardian only uses one combat style (indicated by the colour on them), so pray accordingly. Go west, south, east all the way, north, west, and south. The traps will do more damage than the guardians so be on the lookout for wall traps.
Once you reach the center, grab the key piece. The plinth also activates to for a two-way transport between the entrance and center.