Story achievement / unmissable.
Right at the end of the 'Dinosaur Island' DLC, you obtain the Gold Key, then fly back to the hub; into the ice world; and back to Petey Piranha.
When you've unlocked the final gate, you'll see the exit bot, but it will be destroyed.
Fly back to the hub, and talk to Newton to get a compass. Follow the compass to the first piece of the exit bot, which is just in front of you, high in the sky.
The achievement will pop at that point, and you'll likely have 100% in Dinosaur Island, but it's quick to finish the story as well. Follow the compass to fly through the remaining parts on a lap of the island; then return to the ice world and the bot's original location to complete the DLC and exit the island. It's an extra 4-5 minutes after getting the last achievement.