The Tears of Itlaocol is a mini-dungeon found in Caledon Forest. Your first step is to defeat Veteran Hylek Chieftain. Behind the Veteran you will find three boulders and a gong. Pick up a boulder and throw it at the gong to open the door. Inside, there are several Veteran Hyleks on your path and at the end you will find stones and Tears of Itlaocol. You have to solve a puzzle by putting the tears on the rocks. Look up at the rock face above the small waterfall and you will see glowing dots. Copy the pattern of glowing dots and you will solve the puzzle. Completing the mini-dungeon will grant you the Tears of Itlaocol achievement in the explorer tab.
Wooded Kingdom Moons in Super Mario Odyssey