So, you've explored the dunes and came across a tunnel leading underground. You find a dead end. What now, you ask?

Return to the place where you spawn at with the tree. Go up to the pillar right by the path leading outside the crater and interact with it. A beam of electricity will shoot out of it and towards another pillar; use the pillar that receives the electricity. Then interact with the next one. Keep going until you form a 'ring' around the tree.

Return to the 'dead end' in the cave and you'll find a hole leading deeper inside.