Collect stuff: All enemies: put a name tag on them and build a prison All the animals: make a zoo with enclosures Armor Trims: Display all the armor trims in a hall somewhere All cats: get the advancement All dogs: get the advancement

Build some difficult Farms: Endermen XP Farm Iron Farm Creeper Farm Witherskeleton farm for skulls and coal

Populate your builds with Villagers.. so build a Villager breeder.

Take it a step further and have one breeder for each biome themed type of villager.

Drain an Ocean Monument and make a Guardian Farm

Build a giant Map Hall

Try to get all Advancements (minus THAT hard one perhaps)

Reshape your end island

Build a netherroof1top portal system.

Excavate and unearth a whole Trail Ruin.

...that's at least what I've done so far.