The Supreme Shape
The Supreme Shape is one of the 'Level 4' "Golden" Chamber Dungeons. The chamber dungeon is unlocked after Link completes the Ticking Clock dungeon.
The dungeon has an entrance and a boss lair, but requires link to place 31 tiles down to fill the map. The dungeon is shaped with the letter Z, presumably for Zelda. Similar letter design was including in the original The Legend of Zelda, where Level 5 of the Second Quest was also shaped in a Z-pattern.
Link will earn a Gold Rupee, worth 300 Rupees, for arranging and then completing the dungeon.
The last challenge is another fill-in job. Why this shape? I just like it. That's all. Use it to make a dungeon I'll like too, OK?