Complex sentence: It is widely rumored that the inspiration for this song is Mablethorpe, a once hugely popular sea-side resort on the Lincolnshire coast that has over time become run down and quiet, even in mid-season.
Split into simpler sentences: It is widely rumored that the inspiration for this song is the once popular sea-side resort town of Mablethorpe, on the Lincolnshire coast. Over time, it has become run down and quiet, even in mid-season.