0nslaught

I only found five so far. The ones i found were: 3 from the temple altar 1 from the slith city 1 from the dead slith Just wanted to know if anyone knows where i can find the 6th triangle, i've been going through the whole place for a lot of times now and i cant seem to get lucky. Also, how can you open the box that has no lathces/locks? It is found in the same place as the metal triangles quest. Thanks in advance.