We used a small particle effect in Toxologic to guide the player towards open doors. Since the doors would only open for a brief period, players had to know to chase the effect in order to get through the door. This is the final effect we created.
The path is driven by animation curves the level design team created. I wrote a small script for orbiting the animated game object and attached it to 2 objects along with particle trails. This resulted in some nice, smooth arcs, no matter how sharp of a turn the effect had to take.