(DM NPC POST)
As you walk into the hall and look at the ring attached to the bones, Lukas mentions to you that he feels a very light cool breeze coming from the archway to the left. His gnome instincts and sensitivities can feel such things in the deep caves.
In case you are having a hard time picturing it, these passages are 10x30 breaks in the mist, like this with four archways going back into the mist:
----| |----
| |
----| |----
In this diagram, for example, you entered from one of the long ends (let's say the left side). SO "left" would take you "north" and "right" would take you south.