Where to look for fractured walls?
Solution 1:
Nodes can either have one, three or four routes away from it, never only two. This means the Harbinger node would connect to the node above and to the left of it, since it only has two connecting routes at the moment.
Go to that node and travel the route leading downwards until you come to the wall. Once it blows up you can go back to the cart and the route will be open to travel to it.