Nether portal



The Portal is part of the October 31st Halloween Update.

It consists of a frame of Obsidian, four blocks wide, by five blocks tall.

Once the frame is constructed, the player then sets the space inside the frame on Fire.

This creates a swirly purple vortex inside the frame. When the player stands in the purple vortex for a few seconds, they are taken to The Slip. Stepping through the portal just brings you out the other side of it.



Media
Here are some preparation videos and commentaries in which people craft portals according to Notch's specifications. here and here.

On 10/10/10 Notch revealed the above screenshot on his blog showing portals.

On 29 October 2010 PCGamer released this video, showing a portal being constructed and used.