This one was a long time coming. 75th Trombone was the first (I believe) to decipher the clue, and he and others successfully triggered the egg (see below) but didn't realize it. I came along a few hours later and stumbled into the egg by triggering it and then heading out to the Mechanical Age linking book. Along the way, I happened to look up at the tower and -- BOING!! -- there it was.
The first part of the clue comes from the doughnut egg solution; the second part is another fireplace grid code, but 75th discovered that you enter the numbers counterclockwise instead of clockwise. This gives you two patterns that look like this:
..1111..
.111111.
11......
11......
.111111.
..1111..
...11...
...11...
111..111
111..111
...11...
...11...
The second pattern explains the "plus" in the clue.
The two patterns in succession trigger a gun that protrudes from the top of the rotating tower:
And a flying shot from A'Reandal:
There is a second part to this egg. If you rotate the tower to the stoneship position and then go outside toward the stoneship, look up and watch the gun. After 30 or so seconds, the gun will wiggle and emit a firing sound. So far, we haven't found anything that triggers this other than the passage of those 30 or so seconds.
Like the torsk egg, this one looks like it comes from Myst Mayhem, the April Fools 2000 joke by Cyan that in fact tipped off the existence of realMyst. A picture associated with this joke is here.
