A lot of mobs spawn only in certain structures, this makes their farming much more interesting and sometimes more challenging.
Guardians
Guardian farms are probably the most common large scale farm, because of their relative simpleness and drops, that provide you with unlimited food, building blocks and even a nice light source in the form of sea lanterns. Gnembons designs have been the best for years and he continues to make upgrades.
Wither skeletons
A wither skeleton farm is a mob grinder that involves creating a spawning pad inside a nether fortress, while removing all other mob spawning points nearby.Wither skeletons have a chance to drop a wither skeleton skull, three of which are required to create a wither, which drops a nether star used to craft a beacon.
Witch huts
The heart of all technical servers and the best way to collect large quantities of redstone, glowstone, potions and other useful materials such as sticks. The more simple way is building a contraption, moving witches to their kill chamber and the player standing far in the air to prevent spawning outside the farm. The most efficient way is removing several million blocks to prevent spawning and killing the witches on the spot, this becomes even better when there are several huts within the perimeter.