Crow's Nest is one of the challenges available in The Rustyards.
Objective: Reach the top of the scrapyard ship mast.
The mast is on the scrapyard ship in the middle of the map. Reaching the big cross-bar is sufficient to unlock the challenge. This requires an initial climb up the forward side, a jump across a gap in the corner to a ledge on the port side, and lastly a series of jumps from ledge to ledge at the rear.