Running through the middle of the Emergery is a sizeable river, which splinters off to the north and south, fanning out into a delta as it reaches the coast.

In the middle of all that is a dark, treacherous swamp, which is out-of-bounds for all sane people. It has quicksand and pythons, rotten matter and twisted trees, and lots of black gloop. Numerous nasty creatures lurk in its depths. Sunlight rarely gets in.

The surrounding towns are prosperous from the flood plain agriculture, and they have news services who are well-funded and short on stories, so that annual wizard pilgrimage is predicted, reported on, and then reviewed, making sure that the one-weekend event provides stories across many months.

Of the magical folk who enter the swamp, wizards are the easiest to identify, but all sorts attend the whatever-it-is. Few regular people have dared to investigate, and all those who tried and made it out again, tried following the pilgrims but quickly became lost. Once they are within the swamp, the wizards seem to disappear, or at least move a lot faster than you’d think from looking at them.

Legend has it that a device exists that can track people who travel in magical ways, because it picks up on their trail of fairy dust (or something like that anyway). If someone had that, and lacked commonsense, then maybe they could discover what goes on in there, once a year…