Go right 1, then go left, press “t” and go quickly down towards the key, then to the TNT and light that, and then you’ll be where this picture shows. The 4 diamonds with the balloon is a maze, many times I have pushed it wrongly. Get the 2 top ones, then the one directly above the balloon, go one up one right quickly, push the balloon left and now get all the diamonds in the bottom left corner (but not the chest).
You have two chests to choose from, the correct one is the one hiding the 4 diamonds, get that chest, clear all the diamonds then go to the top. Now go right through the crumble wall (look carefully at the picture) do not go up through the first column of crumble walls!