This is the Endless Sands adventure/puzzle map. What currently exists are the first first four sections of the Labyrinth portion of the Endless Sands map, as well as some of the sixth chapter of the map (City). It's not complete in any sense of the word, but feel free to play through it regardless.
I have written a walkthrough, and it's posted as 'Endless Sands Walkthrough' on fictionpress.

Have fun! Tell me if it works.

Update:
Looking around I found out that this is already larger than almost any maze ever built in Minecraft. Uhhh. Okay.
The floor space alone in the four enclosed sections of the Labyrinth so far total up to 228,290 blocks. If you add in the walls and airspace of the two maze sections that are designed at a constant level, it goes up to 1,064,860 blocks.
This literally might be the largest maze ever built in Minecraft. Whoops. That was not really my intention when I started making this, but... if it happens, it happens. I've still got plenty more sections to build! We'll see how it turns out in the end.