Thanks Both. You can't get inside unfortunately (unless your name is Dan!). The doors are all shuttered. However, I do have contacts with the historical building society in Potsdam so there might be a chance. I keep forgetting to ask.
I do my primary sorting and editing in LR and apply any Nik effects from there usually. However, if I need to correct verticals etc (which is a must for distant shots with the Ricoh) I do an edit in PS and use edit/transform/distort. For this shot, I did some basic corrections (clarity, sharpening, blacks etc) in PS and then edited it in PS to correct the verticals. When saved back to LR (sometimes I do the Nik stuff in PS, especially if I want to combine colour and B&W etc), I did the mono conversion in SilverFX. I then re-opened the file in PS as for some reason the conversion had left a very fine lighter boundary between the roof and the sky. So I used clone/darken to get rid of that and saved back to PS. The I sharpened for output in Nik Output Sharpener and exported the file as a JPEG (85%, sRGB) for upload and sharing.