I tried the above solutions, but had no luck. Some people mentioned that the turtles were random, but I can't confirm that is true. All I know is that what I did worked for me the first time.
I went into Free Roam, which can be accessed from the main menu and selecting
"Special Features" >
"Thorofare Free Roam". Select a save slot and proceed into free roam.
From there, I woke up in my tower, "Two Forks", ready to rock. I followed the video below from BitBytes on YouTube, which I take no credit for and thank him for helping me get this achievement.
If you're in Free Roam, fast forward to get the map location which is shown at 0:38 and then follow the video to unlock it. If you are playing the story, then follow the directions on Day 1, as per the video.
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If you leave a negative vote, please leave a comment so I can improve the solution.