Celestial Pillars

The Celestial Towers are four Bosses that appear during the Lunar Events. There is the Vortex Pillar, the Stardust Pillar, the Nebula Pillar and the Solar Pillar. You have to defeat 100 enemies (150 in Expert Mode) before you can destroy them. The craftable gear from each correspond to the 4 main classes in the game, Vortex for ranged, Stardust for summoner, Nebula for magic, and Solar for melee.

If you exit the game without destroying a Pillar, all progress made will be reset.

Defeating each triggers the following status messages:
 * First Tower destroyed: "Your mind goes numb..."
 * Second Tower destroyed: "You are overwhelmed with pain..."
 * Third Tower destroyed: "Otherworldly voices linger around you..."
 * Fourth Tower destroyed: "Impending doom approaches..."

After defeating all four Celestial Towers, the Moon Lord will spawn.

Tips

 * A quick and effective way to kill all of the pillars is to use the North Pole directly and vertically above a pillar. Even if a player does not have any melee modifiers, if all of the snowflakes can make contact, the pillar should fall in less than 20 seconds.
 * Another strategy is to use the Nimbus Rod as you can leave the place and let it deal damage, placing 2 clouds, you just need to resummon it once, or even none at all. If you leave a nimbus cloud above the tower and teleport away, it will still do damage until either the tower dies or the cloud runs out. Can be combined with regenerative Spectre armor for long distance healing, as the healing orbs have a very large range, extending well from the tower area.
 * Some other weapons might be more effective, but they are not obtainable until first pillar is destroyed. Therefore, if you decide to start with the Vortex Pillar, using the Phantasm will be incredibly faster for the next ones.

Trivia

 * All the pillars seem to consist of Ebonstone Block.