Since the "30 Days" technique makes world-building on the usual fantasy scale pretty much impossible, I have decided instead to select in advance a period that interests me and research it intensively during the pre-writing period. That way, my subconscious will have plenty of material to draw on when it comes to the actual writing. The period I have chosen is roughly 1550-1650, mainly because one of my favourite bits of previous writing was about a group of strolling players. It's a familiar setting for fantasy fans, but just different enough from the standard medieval world to be interesting, especially if I include gunpowder (which often gets omitted from fantasy worlds regardless of their "historical" period).
As it happens, we were planning a trip into Suffolk this weekend, so I have arranged to include a trip to Kentwell, a Tudor manorhouse with lots of reconstructed interiors and farm buildings of the period. This will give me at least one potential location; if I exploit the "crucible" concept fully, it might even be my only location!