The way the process works is you use your Wormhole Generator: Northrend and if you get lucky you get the option of going to the Underground. Once you get the option to you'll get to trade with a vendor named Kaye Toogie, which has multiple rare patterns that are worth anywhere from 250-5,000g.
Keep in mind that you do need some luck on your side, in the past 6 months I've only ever gotten the option of going to "underground" three times. I've always managed to sell the patterns anywhere from 3-5,500g, and all for about a single mouse click once every four hours.
The three schematics are
- Schematic: Arcanite Dragonling
- Schematic: Mechanical Dragonling
- Schematic: Mithril Mechanical Dragonling
So for a couple minutes worth of work you can net yourself an easy couple thousand gold, pretty epic tip/gold making hint huh? Now go use to Wormhole cooldowns! :)