Take the Wyrmbane Spire portal into Shimmersand and head over to /setwaypoint 6354 7747 You need to climb up the hill to get to the puzzle at /setwaypoint 6414 7719 this can be tricky to do so I’ve made a video to show the route.
The Puzzle
The puzzle is a game called peg solitaire, it also has many other names such as Chinese Checkers you need to move the pegs/lights around the game board, when you jump over a peg/light that peg/light will disappear, keep making moves til you only have one peg/light left. There are loads of guides on the internet for how to complete this puzzle, I have consolidated one of them for you..
And a video of the solution..
You can find another explanation of the puzzle here. In this explanation, Miss Mediocre has numbered up all the squares and listed the moves. Some peeps may find this easier to follow than the picture above.
Once you complete the puzzle there will be an explosion and the puzzle will disappear. Where the puzzle was will now be a chest for you to loot, looting this chest grants the cheevo.