Very cool encounters.
Here's a cool one we played recently (from an unnamed published adventure so as not to be a spoiler):
We found a group of kobolds in a forest. There was a small stream moving through, plenty of trees for cover, and a small waterfall feeding the stream nearby. The Kobolds had a magic circle next to the stream (+1 attack for anyone attacking from a square in the circle). It turns out the waterfall was an entrance to a kobold lair. When adjacent to the waterfall the kobolds could attack us with thrown javelins from the inside. Inside the kobold lair was more kobolds, with an experienced goblin commander.