A blot on the landscape
Definition 1 of 1
Pro Tip 1/3Visual Impact
Used when something negatively affects the beauty or visual aspect of a place. 
The garish billboard is a blot on the landscape in our quaint village.
Pro Tip 2/3Not Literal
Can be metaphorical, doesn't only refer to physical landscapes but also to situations or contexts. 
His unethical behavior was a blot on the landscape of the company's reputation.
Pro Tip 3/3Negative Connotation
Expresses disapproval; what is described is usually considered unsightly or undesirable by most people. 
The dilapidated building is a real blot on the landscape of the high street.