Geographical Barriers

[SpikeFightwicky]

I'm not really much of a geography connoisseur, but I was wondering what kind of 'natural' terrain or weather (or mix of both) would be able to block access to a part of the land at the same time every year (preferably during the fall, lasting until the end of winter).

More information: A valley lies nestled among the mountains in the northern part of the world. The main access to the valley is through a (insert natural chokepoint here - like a canyon, bridge or a rough mountain pass) which becomes closed off during the later times of the year due to (snowfall? heavy rains?). Being the only direct path into or out of the valley, whoever's still in the valley at this time must wait out the fall and winter months until spring arrives and (effect melts or washes away or something), unless they feel brave enough to traverse a large peat bog to reach an alternate mountain pass that may or may not also be blocked off.

Basically, I want to make a secluded valley area that get sealed off from the outside world for about 1/3 of the year because of some natural occurence (nothing sinister, just regular nature at work). It should be something that mid-level magic could not feasibly clear out (I know teleporting is a workaround, but I already have other plans for that).

Any suggestions or ideas would be greatly appreciated.

[Enguhl]

Heavy rain/snowfall block the canyon/flood the river/mudslides.

[AKA_Bait]

Wildfires work too. They don't need to rage the whole time but scrubland that could go up any moment would certianly discourage travel and trade part of the year.

Also, considering we are working in a magical world, regular earthquakes or chasms opening up is not out of the question either. Nor is a perpetual very dense (or even poisenous) fog over a large area.

[Mr.Moron]

It could also be mating season (or some other comparable reason for them to grumpy) for normally docile but extremely powerful breed of critters that are common in the area. Most the year can you can walk right by the 1000ft tall, lava-breathing brutes that use trees for toothpicks, but during those couple months probably not such a good idea. It's not exactly the terrain, but it is very natural!

[SpikeFightwicky]

Awesome ideas! I think I may have solution may incorporate a bit of everything.

How does something like this sound:

Near the end of Summer/start of Fall, heavy rains sweep through the valley and causes flooding in the bog. This flooding causes the release of a thick mildly-toxic mist from the bog that wafts into the mountain pass and stays there until spring meltings drain most of the excess water in the area into the main lake and eventually out to sea. For good measure, this part of the season marks the start of the active period of the usually dormant bog ecosystem (consisting of some poison immune creature... maybe vermin? -> the main predator of that ecosystem) which hunts in the bog as well as any fogged over area.

[ryuteki]

A book i read had a valley that was only accessible by a secret "land bridge" that was under water all the time, but the inhabitants knew where it was (it was where they retreated during wars), and could traverse it except when the water was running high during the winter and spring. It was of course also reachable by boat, which I don't think solves your problem, but it was interesting.

Probably your best bet is some sort of magical storm that sweeps in for the winter, something like the Pelagir Hills from Mercedes Lackey's Valdemar series. Take your average blizzard and/or heavy thunderstorm, up the lightning strikes, and throw in wild-magic effects (take your Wand of Wonder table, and replace most of the positive effects with lightning strikes. Apply that to lightning, random encounters and any magic used by the PCs). Base the likelihood of a target being struck on how much magical potential they carry (or possess inherently), and also how much metal is on them, and you'll do a good job of keeping them from wanting to go through, but provide a plausible reason why a peasant MIGHT occasionally be able to make it through (if necessary for story reasons). I know it's not exactly "normal" but normal takes a beating in a magical world. At least it's not the result of a spell or trap or anything.

[Megafly]

Does it have to Be Winter that makes it Inaccesable?

in the book "Into the Wild" the man is trapped by a river that swells when snow melts in the summer.

Also, you could have a Glacier in a Mountain Pass that is only safe to pass in the Winter when it is frozen solid. It would crumble under you and dump you down the mountain if you tried to cross it in the summer.

[seedjar]

Bogs and swamps often swell and become impassible during wet seasons - fall and winter in the stereotypical temperate wilderness. Some types of wetlands and grasslands are prone to sinkholes at certain times of year. A desert can become impassible any time in the year, if the clouds shift away for some reason. In the winter, many deserts freeze over and some see ice storms or heavy snows. Winds can be very seasonal, and you can build off of that. Any terrain becomes a hazard in a heavy storm. A peaceful mountain forest could, by D20 standards, become quite the deadly situation, with high winds and reduced visibility - old growth conifer limbs can be the size of small pine trees; 500 lbs to several tons of falling damage, of the bludgeoning or piercing variety. Throw in some exposure to induce fatigue (through frostbite.) I'm particularly fond of the use of weather or other seasonal effects, like animal/monster migration, as they're a tempting option to players, but as a DM you're free to shut them down if needed.
Awesome thread, great idea Spike.
~Joe