First you must complete enough of the main story to have access to the Deep Dive syringe.
Once you can craft the syringe, do so by collecting the necessary leaves.
Head to these coordinates: X:754.9, Y:655.0 (there will be an artifact at the bottom of this deep hole)
Stab yourself with the syringe and take the dive downwards. The trophy will unlock by the time you hit the bottom and grab the relic.