Go to the top mineshaft at night time, then left to the edge, there will be a slight indent in the cliff on the right side, land on it and reveal a secret room where by inspecting the boxes you'll find the scene!
After Mandilitrio makes mention that he wants to make a statue of Calen, climb up in Mandilitrio's cave and in the nook over where he usually stands will be a WIP statue of Calen.
so you don't need to go into the actual mineshaft, you just need access to the top entrance, then follow my previous instructions and you'll find the scene, hope this helps 👍🏻
I tried going to the left but I'm confused by "there will be a slight indent in the cliff on the right side, land on it and reveal a secret room". I'm going left but there is no "indent" anywhere where I can fall. The only boxes I find by going left are two boxes next to a wall.