We send Mara off with our lightning javelins to guard the caravan in case
any of the fleeing cultists decide to make trouble and chase after the
fleeing fire cultists.  Their being mounted and us not puts at a bit of
a disadvantage in the pursuit as they leave their bugbear allies behind.

We head back to Redlarch to resupply before attacking the Spire.  There's
a wedding going on, but it's been disrupted by an air cultist with a
young adult green dragon, and the orb of destruction we'd last seen at
the air/fire meeting.  We take them down, and manage to get the Araqa to
take the (now active) orb far away from the village before it detonates.
4350/6.5 xp, 1500/6.5 xp quest reward.

After the wedding (and a long rest), we head off to the Spire to once
again search for an entrance to the underground sections.  We know it's
got to be around here somewhere as we overheard the air cultists talking
about it.  11 gp, no entrance.  Giving up on the Spire itself, we check
what can be seen of the surrounding area from the Spire, and the go check
all the nooks and crannies of the nearby viewable landscape.  Success!
A nearby gully has an opening to a passage that appears to lead quite
a ways down.