You actually have to place the TNT on the redstone blocks at the top of the labyrinth entrance. The one in your screenshot is just an accidental hole that never got covered up when building the map

if you mean the weeping angel level, you'd have to get to a ladder at -109 59 -93 to go under and the shard is at one of the corners of the maze.

but if you meant the mansion level, to get to the vault, you have to make a scaffolding by getting the bamboos from the pots around the mansion, and then place the bamboo on the stripped spruce wood near the big flat bookshelf on the 1st floor to get onto the dark oak roundel door, inside is a lever. Next, find the lectern on the 2nd floor and go to the last page, the page number of the book mentioned in the book is the passcode to the vault. After that just push the buttons in left to right order