Where to go
The target is in the far south of the island, around the rocks beside the broken railway. A blue structure and a nearby multi-light puzzle confirm that you are in the correct area.
Use the map grid to find coordinates 4166 / 1899, reach the rocks south of the broken train, and hold the hidden button while a teammate claims the totem.
Finish Red Tower and collect its map, plot 4166 / 1899 on the southern grid, then travel past the blue rail-side structure and broken train. Search behind the nearby boulders for the hidden yellow button. Keep one player holding it while another waits at the reward case and collects the totem.
The target is in the far south of the island, around the rocks beside the broken railway. A blue structure and a nearby multi-light puzzle confirm that you are in the correct area.

Read the two values on the puzzle board as one map target: 4166 and 1899. Do not treat them as a button sequence.
You should have the pair 4166 / 1899 written down before opening the map.

Open the Red Tower map and use its numbered grid to match 4166 on one axis with 1899 on the other. The intersection falls in the southern part of the island.
Your marker should sit well below the island centre, not near Red Tower itself.

Head south toward the railway. If the train route is available, use it to cut the travel time; otherwise follow the map on foot.
A blue structure beside the railway appears as you enter the correct southern section.

Continue along railway line 41 until you find the broken train. Look for the rock formation near the separate multi-light puzzle.
You should be able to see the broken railway area and rocks within the same short walk.

Leave the obvious path and circle behind the nearby boulders. The yellow button is low to the ground and easy to miss from the railway side.
The interaction reticle appears over a small yellow button tucked against the rocks.

Keep the button held down. At the same time, have your teammate wait beside the reward case and pick up the totem as soon as it unlocks.
The reward case opens for the waiting teammate; releasing early can close the window.
Send one player to the rocks and leave the other at the reward case. This is the fastest reliable setup.
Keep the same two roles; extra players can scout the railway and boulders so the button holder reaches the spot sooner.