Found an old kitchen behind the wall!

[TiP]

Kattvind?

It probably is.

 

[TiP]

It looks like you have found the attic space. There should be one along the entire side and also on the opposite side of the house.

That could be it, I probably won't dare to look in more places... maybe they put the bathroom there or something !?‍

 

[Jonas_81]

Ikea's large blue bags are very practical for carrying out demolition debris.

Byggmax has yellow and slightly more stable ones

 

[Orientexpressen]

I don't think there are any pipes or electrical wires back there except for what should be there. They probably just put all the debris there to fill out the space or they didn't know what to do with everything. It's strange. Contact the building committee, they might have blueprints of the house. You can also measure the outside and then the inside and see if there is a significant difference.