Okay so as for the fey crossing lets work that underneath said bridge are several carved stones buried beneath the streams water and muck and when the bridge is crossed upon a certain time of the month/year under a full moon the players are transported into the fey lands. Traveling a ways the players soon come across a village/town situated in a small hilled valley with the inhabited parts sitting behind a log wall. Outside the village town are buildings covered in fungus, vines, and overgrowth... perhaps the players will encounter some crazed wood type fey that tries to kill them and they fight their way to safety of the village. Once inside they could be asked to find out the status of those at a small fort built over the entrance of a mine... x-miners live their... only to find the mine is now overrun with some monsters, kobolds/goblins, and must clear the mine out fro the villagers and free the remaining miners. Deep within the mines lowest level the players eventually find what is causing the fey to go crazy
I'll work on this some more
Addendum
Eventually at the end when the players cross over bridge and return to their starting point or initial destination, the Capital, they could find from the local lore-keepers that x-centuries before there was a village and mine but some unknown catastrophe befell them destroying both in a certain year... further investigation could reveal that the players were there x-years before said catastrophes happened. Fey Magical Portals dealing with time travel for the mind breaker... maybe the Fey need the players to stop said catastrophes.
I like where you're going with this--it's got the potential to be a great campaign starter! Unfortunately, I've only got a 4-5 hour block to tell this story; as a one-session adventure, it's not technically an ongoing campaign. I'd need WAY more time to do this story arc the justice it deserves. That being said, I'm totally banking this idea to use at a later time!
I think I've figured out what I'm going to do. I've scrapped the witchy idea and went with the fey crossing. Let me run it by you guys and see what you think. Because of the time constraints, it's kind of rail-roady and super linear, but that's the way it goes this time..
They basically find the bridge in the middle of summer, have a nasty battle there and figure out it's a portal. Go through it, have a nasty battle on the other side with a yeti. A yeti? Yes... they've crossed into the Summerlost Woods in the feywild, where it's always winter. Since they're dressed for summer, insert environmental factors here.
They hear screams, blah blah.. find a half-dead centaur that manages to tell them the story of an ice witch who beguiled her lover a year ago today when she waged war on the fey of Summerlost. Over the next year several redcaps have sprouted from the bloodshed, and it was one of those redcaps who attacked the centaur. Then she goes from half-dead to full-dead in true cinematic fashion. They will be able to track the redcap easily enough since it will be dripping fresh blood on white snow, and they always seem two steps behind it as they encounter the carnage it's causing in the forest. A few encounters later they finally track the redcap as it has just made a bargain with the ice witch. She then sets the redcap on the PCs in an arena-style battle while she sits upon her ice throne and watches. Caveat: the redcap has a partner--a beguiled centaur! Since the enchantment can only be broken with love's kiss, and his lover is dead, queue tragedy as the PCs have to kill him. Ice witch gets mad and monologues for a bit, says something about
I'll do it myself and we have a climactic battle has the PCs resources are dwindling.
It's a lot, and I'll stock them with a few healing potions before hand, but I think they'll make it. I've modified the tougher monsters to suit their level so it's not too overwhelming, but it'll still be tough. I hope. Somewhere along the line they'll meet a pixie who they may see again, but that's another story...
What do you think?
-IG