4)Write it up as much as you like

• Create a map or visual (maybe)
• Detail each area/room
• Subdivide as needed
• Make lists and tables
• Make plans
• Review and revise

You don't need to do this entire process, or do it all at once. If pressed for time, do only as much of the process as you need for the next session. Improvise the rest, and finish later if it's relevant.

Last session, the PCs lured a curious construct into a site north of Three Coven Lake. I laid the foundation during play, picking an example site from Book II*: "warren of rooms carved into a bluff. Once a Stone Lord's manor, then a warlord's fortress, finally the site of her demise." I made up details as the PCs set their ambush, and we ended there.*

Between sessions, I flesh out this warren they've found themselves in, building up its story and sketching out some contents. I suspect that the PCs will make this their base camp, so I even draw a map.

I still need to decide what this construct's deal is, and figure out where in Three Coven Lake the PCs might find the Mindgem's fiery heart (the whole point of this expedition). I bet they're related! I lay the foundation for the heart's resting place: a reclaimed tenement north of the bluffs, home to a deathless sorcerer whose mind is spread among a number of lithic servants (all powered by the fiery heart). I write up the sorcerer, but don't bother detailing the site yet—I doubt the PCs will get there next session.

Instead, I create a few other areas the PCs might encounter first: a haunted workshop, a broken obsidian mirror, and the home of an exiled Hillfolk spirit-talker (the sorcerer's rival). I'll flesh out the sorcerer's complex after the next session.