Nether Reactor

The Nether Reactor is a structure built using a Nether Reactor Core - a block.

Crafting
Crafting the Nether Reactor Core requires three diamonds and six iron ingots.

Nether Reactor
The Nether Reactor is built with a nether reactor core, 4 gold blocks, and 14 cobblestone, arranged in the following configuration:

Top layer:

Middle layer:

Bottom layer:

When the Nether Reactor is built and the core activated (by clicking), it generates a room of Obsidian (7x17x17) with some openings, around the reactor called a "Nether Spire" (unofficial name). The blocks that make up the reactor, excluding the core, will turn into a new block called Glowing Obsidian, and it will start spawning various items and blocks, such as Gold, Melon Seeds, Paintings, Glowstone Dust, Doors, Mushrooms, Bones, Cacti, Arrows, Feathers, Bowls, Sugar Cane etc., as well as Zombie Pigmen. After it burns out, there will be a massive obsidian structure with multiple floors. The bottom floor is hollow (all blocks inside other than the reactor are replaced with air), and the upper floors retain the blocks that were already there (air for an above-ground spire, dirt/stone/etc. for an underground spire). The core is still there, and is reusable. When the reactor is active, the core's texture will change to red, and after it burns out, it will change to a blackened texture.

The Nether Reactor only lasts around 45 seconds. During the 45 seconds the Reactor is active, it is difficult to escape the room, as it is all obsidian. Once about 5,10, or 15 seconds have passed, the time sets to nighttime, so left over items in the room can despawn once the Nether Reactor stops.

It destroys any block that happens to be in the way of the room

Bugs

 * If placed at bedrock, when the reaction occurs, it will remove the bedrock if it is not placed too low. Using this, one can access The Void in survival mode.
 * If you mine the core while it's active,it will remain active and it will remain night time. When you go to sleep, it will turn to to day, but will shortly turn night after awhile. Exiting the world should stop this, but the core will remain on.
 * A burnt-out core can be reactivated by leaving it in place and rebuilding the reactor pattern around it. This produces an effect similar to the effect produced by removing the core while it's active.

Trivia

 * The Reactor does not function in Creative mode; this is intended.
 * The reactor's structure was originally iron and gold blocks rather than cobblestone and gold, but this was changed due to its cost and the fact that the reactor turns into obsidian except the core.
 * The air blocks in the pattern are not optional. This means you cannot build the reactor underwater unless you waterproof the air blocks in the pattern.
 * You can quickly mine some or all of the materials out of the reactor after activation and it will still function, this way you can recycle the expensive Gold Blocks. Another alternative method is to simply have a friend help mine the blocks right after activation. If you're fast enough, you'll have time to mine all four gold blocks with a diamond pickaxe before they turn to obsidian.
 * If you construct the reactor near a world edge and activate it,you will see it turn night.
 * There is an elevation limit for the reactor, above which it cannot be activated.
 * If you want to hide the spire produced by the reaction, build the reactor deep underground.