you can download the Portal mod via the official Minecraft forums. Which I assume no one reads any more. The mod and video were created by forum user iChun, and the post there explains how to ...

One Minecraft creator has rebuilt Portal 2, using the tools available to every player. A Minecraft player by the name of Lag Master163 put together the Portal 2 map featured in the video below.

There are two major kinds of portals in Minecraft: The Nether Portal and the End Portal. To make a Nether Portal, you'll need at least 10 obsidian blocks and some way to light them on fire.