The four Celestial Pillars

The Solar Pillar is the melee-themed pillar and the most difficult. You must stay grounded to avoid spawning a damaging worm enemy that can only be damaged on its tail. While grounded, you are vulnerable to charging ground enemies with high health and contact damage.

The Stardust Pillar is the summoner-themed pillar and the second most difficult. It features a worm-type enemy vulnerable only on its head, and multiplying Star Cells that complicate combat.

The Nebula Pillar is the mage-themed pillar and the third most difficult. It has enemies with attacks that pass through blocks, and one that can attach to you, severely limiting vision.

The Vortex Pillar is the ranged-themed pillar and the least difficult. Its enemies move quickly and shoot fast attacks, requiring constant dodging, but lack the extreme threats of other pillars.

For each pillar, you must first kill 100 enemies (150 in expert mode) to remove its force field.

Once the force field is down, you can attack and destroy the pillar.

Repeat this process for all four pillars. You can tackle them in any order, but they have a difficulty tier list from most to least difficult: Solar, Stardust, Nebula, Vortex.