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.
You come upon a ruined building in the back section of a city park (or other out of the way area of the city). The ruins are fairly overgrown. All that is really standing is a doorway and its frame. If you pass through the opened door, you travel to a different world. If the door closes, there may not be a doorway back to get you back.
Every now and again, the region encounters a dense blue fog. Every now and again, things disappear into the fog never to be seen again and things appear out of it from other places or world. It seems the fog is the material form of some minor diety charged with moving things around the universe to balance cosmic forces.
While travelling near the edge of a forest the air is filled with the wailing of battle horns. Soon a large group of mounted cavalry will gallop by in a panicked rush. Some will spot the party and shout "Flee! Flee for your very lives!"
Several minutes later, hundreds of running infantrymen will be spotted. A large group of white clad knights fiercely chanting a battle song is in full pursuit. One of the white knights carries a banner of a white horse on a black background. The horse is rearing under a gold crown, indicating the presence of the Paladin Prince. As the horrified infantrymen struggle to flee into the forest, the zealots charge into their midst and cut them down by the tens and hundreds.