The alternate quality Portal gem, Anomalous, introduced in Heist has an interesting quality effect.
Quality Effect: (0.00-0.20)% chance to travel to Winding Pier instead while on a Ley Fishing Line.
This gem can be obtained from sources that provide alternate quality gems, noteably Grand Heist blueprints Repository and Tunnels which provide unusual gems as the reward. Additionally, these specific Grand Heists can offer a Prime Regrading Lens to convert a regular Portal gem into the anomalous alternate quality.
If Heists aren't your thing, buying a Prime Regrading Lens and using it on a Portal gem will often be cheaper than purchasing an anomalous portal gem.
Before blindly casting Anomalous Portals and entering them, consider the condition that the gem states: "[...] while on a Ley Fishing Line". Try to guess what a "Ley Fishing Line" might be before making your attempt. Without a solid lead, you will likely choose an incorrect location and waste a lot of time.
Note that the wording states "[...] chance to travel [...]". This may mean you must enter the Portal (not merely cast it and hope that its label name changes).
Improve the gem's quality to increase the proc chance. Any standard method of improving gem quality will work. Some methods include:
It's possible that there is no such thing as a "Ley Fishing Line", which would make Anomalous Portal's modifier useless. Test at your own risk. Good luck!
Due note that legacy or sythesized standard items may be able to increase the quality over 100%. This image was posted by Epsi in the Fishcord.
The typical setup is crafting an item with multiple + level to support gems and using a corrupted level 4 enhance to increase quality further.