You’ll need to sneak in the NERO landing zone. You can’t hurt or kill any of the NERO operatives but you can use stealth and distractions to keep them away from you. To start off, use your binocular to mark the visible operatives so you can track their movement. Go down the path and distract the first operative by throwing a stone away from him.
Once he leaves his post, sneak past to the left and circle around the big rock while hiding the vegetation. Wait for the operative there to walk away then quickly move while hugging the rocks to the left (take note of the historical marker for now) until you reach the wooden platform.
From the wooden platform, stay to the left to ensure that the generator behind you will block the previous operative’s line of sight, then vault over the ledge down to the vegetation below.
Carefully approach the yellow circle near the Cave’s entrance to start eavesdropping on the researcher. Make sure to stay away from the edge of the bushes to avoid getting spotted by the lone guard. Stay in your position until the researcher relocates to another spot.
Carefully follow them and use the rock pillar to circle around the guard and avoid detection. Once you’ve heard enough, you have to backtrack to where you came from.
Turn around and sneak through the bushes around the wooden walkway earlier. Wait for the lone guard patrolling the historical marker area to leave then quickly examine the marker if you want (Grotto Caves - The Buried Caves).
Continue forth while hugging the rocks to the right. Move to the big rock to the left next as you move forward. The last two operatives are the only obstacles to your freedom. First, let the patrolling one leave then use a rock to distract the stationary guard. Slip past them and continue heading uphill. Return to your Bike to complete the mission.