The end is near. But before you can enter this area, you must first complete at least 5 of the 9 main areas. Preferably, the one with the diamonds (Mines), the die dots (Shrine), the flower petals (Gardens), and the lines (Mill). Then you'll have to solve a puzzle at the entrance using all four of the aforementioned elements.
Once inside, more puzzles will have to be solved, but there is a twist. All of the tiles on each puzzle board cannot be changed to black or white. Instead, you'll need to place each puzzle element onto the board. Satisfying each puzzle mechanic within the adjacent tiles. As you progress, they'll then need to be aligned with all 3 puzzle boards at once. Remember, trail and error will be necessary so take your time with these.
Once all 4 sections are complete, go to the tree at the top and click on the tile in between.