The Crow's Nest is the eighteenth and final level in Rayman 2: The Great Escape. Both levels of the Crow's nest, are fought on/in the Prison Ship. A size comparison at the start shows just how big the ship is. The tiny pole, barely visible at first sight, is where the entire level of the Crow's Nest takes place.
The first phase of the Crow's Nest, requires Rayman to avoid the Grolgoth, who shoots cannonballs, and tries repeatedly to slam Rayman. Unlike any other levels that have the boss battle at the end, this level starts with the boss battle..
After this, the Grolgoth breaks a hole in the mast, and both it and Rayman topple down together. Ly, the fairy, saves Rayman, and leads him to his flying friend, the shell. The level gets a bit harder as you have to ride him, and shoot the all too stable Grolgoth into the lava. And, if that wasn't hard enough, you have to avoid hitting into the walls, rising lava, and avoid getting shot by homing missiles.
There is an easter egg here that will give you unlimited ammo.
The PlayStation version is entirely different. You are chasing the Grolgoth down the passage, and you can move in eight directions avoid attacks, since the rocket is going after the Grolgoth by itself.