What is this purple magic effect in the starting town?

[ErikW]

Shows up in solo and in coop. Not sure what it is or why it happens. It's there permanently though. Is there an npc that fell through the ground? Not causing any trouble yet that I'm aware of, just weird.

https://steamcommunity.com/sharedfiles/filedetails/?id=1706441201

[Harag]

To me it looks like you use to of the rune symbols which created a trap. If you reuse the same 2 symbols it will put down another one and remove the previous one as you can only have 1 trap. It will go when a monster walks into it.

[Galdr]

you can also use the orange rune x2 to explode it

[robruckus65]

Yea its a rune trap it will stay in a town forever unless you manually detonate it.