Solve Maze:
Layer 1
 _ _ _ _
 _ X X X
 _ X X X
 _ X X X
Layer 2
 _ _ _ X
 X X X X
 X X X X
 _ X X X
Layer 3
 _ _ X _
 _ X X _
 _ X X X
 _ X X X
Layer 4
 X _ X X
 X _ X X
 X _ X X
 X _ _ _

Solution:
Layer 1
 R R I *
 _ X X X
 _ X X X
 _ X X X
Layer 2
 I L L X
 X X X X
 X X X X
 _ X X X
Layer 3
 R I X _
 _ X X _
 _ X X X
 _ X X X
Layer 4
 X D X X
 X D X X
 X D X X
 X R R E