End spike

Obsidian pillars, also known as obsidian spikes or obsidian towers, are generated structures in the End that are made of obsidian.

Generation
Obsidian pillars generate naturally the first time the player enters the End, and regenerate when the ender dragon is respawned.

If the End biome is used in the overworld, obsidian pillars will generate without bedrock and end crystals, only obsidian, with some of them containing iron bars. Obsidian pillars generate near coordinates 0,0. If the terrain is high enough, obsidian pillars can generate buried or inside caverns but will generate air blocks around and on top of it. If End biomes generate next to other biomes near 0,0 only some obsidian pillars will generate.

Structure
Obsidian pillars are composed of obsidian, with a single bedrock block and an end crystal on top of each pillar. They have circular forms.

The following 10 pillars generate in a 43-block radius circle around the exit portal in a random order:
 * A 3-block radius pillar ending at y=76 (total of 1596 blocks of obsidian);
 * A 3-block radius pillar with iron bars ending at y=79 (total of 1659 blocks of obsidian);
 * A 3-block radius pillar with iron bars ending at y=82 (total of 1722 blocks of obsidian);
 * A 4-block radius pillar ending at y=85 (total of 3145 blocks of obsidian);
 * A 4-block radius pillar ending at y=88 (total of 3256 blocks of obsidian);
 * A 4-block radius pillar ending at y=91 (total of 3367 blocks of obsidian);
 * A 5-block radius pillar ending at y=94 (total of 5358 blocks of obsidian);
 * A 5-block radius pillar ending at y=97 (total of 5529 blocks of obsidian);
 * A 5-block radius pillar ending at y=100 (total of 5700 blocks of obsidian);
 * A 6-block radius pillar ending at y=103 (total of 9167 blocks of obsidian).

The bottom of all pillars are at Y level 0, which means that pillars are generated through the island.

The second and third shortest pillars include a cage comprised of 73 iron bars surrounding the end crystal, to protect it from projectiles.

$$, the end crystals on the two tallest obsidian pillars are surrounded by iron bars.

Video
Note: This video was made before 1.9. Since then, only ten obsidian pillars generate in a circular position with the shortest ones caged in iron bars.