It just takes a little thought and a little timing
I used Janet Galle's texture, 'urbanscape', which has been used before. Thanks
Michelle
Exactly the way I did it.The idea was to take the canon fire and use the reflectors and prisms to guide the fire to the barrel blocking the exit in the upper right hand room.
This would be quite complicated to describe just in words, so I needed to number all prisms.but I cannot see how you finished this without using prisms