Not sure when it was build but 1900 sounds about right.
The bathroom in particular is probably the coldest room in the entire house. It wouldn't surprise me if it was a drainage issue mind as there is a downpipe from the gutter on the problem corner but it's cemented into the ground so I can't tell if there's anything wrong with it. I've lived in the house for 6 years so the landlord hasn't had an opportunity to cover it up.
On my last inspection from the letting agent they actually appear to have decided the mould issue is a problem that requires fixing - talking about extractor fans and redecorating although I don't really expect either to have a massive effect.