Nether Portal

A Nether Portal is a player-built structure which, when ignited by Flint and Steel, becomes a way for the player to travel to the Nether dimension. It was added in Update 0.12.1.

Construction
A Nether Portal can be constructed primarily by placing Obsidian in a 4x5 block hollow rectangle, however, it can also be created in up to a 23x23 size. The Player needs at least 10 obsidian to make a Nether Portal.

Trivia

 * Bug: Skeletons are able to shoot Arrows through the portal at the Player.
 * Most Mobs and items can pass through the portal and teleport to the Nether, and vice-versa.
 * The Player cannot use a Nether Portal in Old Worlds, as there is no compact "Nether" dimension in Minecraft PE yet.
 * To travel to the Nether, The Player has to build a Nether Portal in an Infinite World.
 * A Nether Portal can be activated by using Flint and Steel using a Dispenser.
 * Before the Nether was added to Minecraft PE, there was a manufactured structure called the Nether Reactor which generated a "spire" of Netherrack with nether-related items inside.