Fearless or StupidG 15

A good place to earn this achievement is at the coordinates X:754.7, Y:654.6 at the Southeastern corner of North Island. There's a Relic at those exact coordinates that you will have to swim deep down in the ocean to get, more than 60m. If you don't have the Deep Dive syringe available you might not make it back to the surface in time and die after grabbing the Relic, you can make it if you swim fast enough but if you do end up dying that's okay, it won't void the achievement or anything.