Star Destroyer

The Cultist's death raises four Celestial Pillars across the map - Solar, Vortex, Nebula, Stardust - each shielded until you've killed enough of its minions (100, fewer in multiplayer). Take them in the order that suits your build's counters, and treat Solar's crawltipedes with respect: stay grounded there. Each pillar drops fragments for endgame gear; the fourth pillar's fall starts the Moon Lord's one-minute countdown (Champion of Terraria), so bank your gear before pillar four if you're not ready.