Mac Dictionary defines it as:
something, esp. a building, that is very large and is considered unsightly : the shopping center, a multistory monstrosity of raw concrete.
• something that is outrageously or offensively wrong : he rebelled against Nazi monstrosities.
• a grossly malformed animal, plant, or person.
2 the state or fact of being monstrous.
There are many monstrous things in this world. How about the monstrosity that is the ROM (Royal Ontario Museum) or has that now been considered art?