Help with this cube counting Q

[super112]

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Here's the imgur url: http://imgur.com/GE0T5ql

I've been looking at this for the last couple of days but it still hasn't clicked. I feel like a small line is missing behind the tower. Can someone help me see this structure correctly?

 

[Ame535]

I don't think it's missing a line. The missing part is not behind the tower it's to the left. Simply there is no cube there just like the one I circled. I hope the picture helps.