Golden Cubes are collectibles that are found throughout Campaign and Campaign+. Each campaign level contains one cube, each worth $300 when destroyed. Destroying all Golden Cubes unlocks a gamer picture for Xbox Live.
A second set of Golden Cubes are present in The Kaiser's Battle DLC. Collecting all the cubes unlocks the Base Rat Achievement.
Langemarck (1914): To the left of your emplacements, there is a cemetery. The cube is in the top right corner. Use a mortar to hit it.
Gheluvelt Chateau: Directly across the map from your base you will see a large German flag. There is an enemy barrack just to the left of it. The cube is on the right side in the north corner. Use a level three howitzer to take it out.
Nonne Bosschen Wood: If you scroll across to your large square emplacement place furthest from your toy box, you will see two crash jeeps just to the right of it. A bit past that, you will see the cube covered by a piece of fallen fence. You can use the closest emplacement spots to use a mortar to reach it.
Fort Vaux: You start this level off right at the bi plane, just hop into it and pull a U-turn left. Fly right towards your toy box. Its on the roof in the corner right of the doorway. Shoot it down, blow it up are just crash into it.
Hill Cote 304: There is a tan castle looking building on the enemy side that sites in front of a bridge. On the back right corner, the cube is on a ledge. You can try and reach it with you bomber plane, but you might get shot down by their AA gun. It's safer to just build a howitzer and fully upgrade it to reach it.
Fort Douaumont: To the left of your toy box (on the side with the bomber plane), you will see a bridge. The cube is hidden underneath the bridge. You can reach it with either one of your planes or a mortar.
Zero Hour 07:20: The Whippet tank is located about half way across the map from your toy box on the left side. The cube is directly behind it inside the broken house. Hop in the tank and and destroy the cube.
"U" Day: To the right of your sniper tower will be the remains of a few structures. The one closest to bottom right corner of the map has the cube sitting inside its broken walls. Send a mortar its way.
Battle of the Ancre: Click the RS stick in to go into a birds eye view of the map. The golden cube is in the bottom right corner of the map across the bridges. Drive the tank over to it and collect it.
Langemarck (1917): This one is a bit hard to desribe, but if you click the RS stick in to go into birds eye view it will be a little easier. Follow across the bridge from where you start off at. Continue up the road and on the right hand side you will see a long building with no roof on it. It has about ten or so rooms inside it. At the back end of the building the cube is sitting under the awning. You will need to drive a tank over to it.
Polygon Wood: Drive the tank you start off with down the path as soon as the level starts. The cube will be under the third bridge you go under. If you keep moving, you will get to it well before soldiers make into your toy box.
The Spring Offensive: Hop into the Whippet tank and drive it into the river on the left. Follow the river north and the cube will be under the bridge closest to where the Rail Gun emerges from.