A seeming endless melee of carnage and killing. As the minecart goes around the outer wall, it hits detector rail to spawn more and more mobs.
You start with great loot- diamond armor and sword, bow and arrows, and a stack of steak. There are other chests in the main tower, containing flint and steel, potions, and other things of the like. When you hit the button to begin, the mobs will begin to endlessly spawn. For a respite, head to the top of the tower to enchant your diamond equipment with the XP you earned from smiting zombies.
Please don't loot dispensers, and occasionally the minecart with glitch out and stop, so you may cheat to start it again.
Post the XP level you were at when you decided to rage quit in the comments.
Special thanks to Pokedudejr (lovely username) for so much help with the construction.