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.
By late afternoon, the sky starts to cloud over. The sun shines behind the fluffy clouds, gilding the edges and showing a Jacob's-ladder of rays streaming through the gaps...very pretty. Gradually the clouds shift into a new configuration: you realize with awe-struck, preternatural clarity that the clouds form a map of a coast-line that you know against the blue sky as ocean: surely it's a Sign! Suddenly, the golden beams coalesce into one long ray that strikes across the blue. A star-like gleam flashes under the ray: perhaps it is an island? But the charts show no island there...who would want to hide an island? Who could do it?