Puzzle 18: Barns 2

This one is really quite hard. There is a hint available.

Puzzle 17: Barns 1

A new Nikoli type that I have not published before: Barns.

Instructions:
Draw a single loop through all of the cells of the grid, that does not cross itself outside of the shaded area, does not change direction inside the shaded area and does not cross any thick borders between cells.