The Marches be a vast sea of grass dividing the civilized parts of The Land.
Corvis is a western region of The Land, comprising several small counties. It is a magical place, filled filled with fruitful farms, green rolling hills, low stone walls built up over centuries, and a number of small forests. The people are happy and content. It is an ideal place.
Most of the time. And it depends on what you think is ideal…
It seemed like a great place to camp. The clearing was good sized and sheltered from the wind. The brook just a few feet away. There is a natural hallow to keep the horses.
Then the night came.
It was like it became a different place. The temperature dropped. The wind, which does not seem to disturb cloth, almost cuts through you like an arctic wind. No one can sleep, as the soft ground has turned hard. The horses are uneasy. The Bats are flying over and stopping in the trees.
And then there is the eyes. There are glowing eyes just inside the tree line watching your group. The mages and clerics can detect nothing, but there is still something there.
(yet there is nothing at all... The Darkness will do nothing unless the players do something to it. And even then it will all seem to be a conincidence.)
Of course, in the morning, it all becomes sweet and light.