Sometimes you want to place an obvious trap or barrier somewhere, but you’d still like the PC’s to encounter it. One way to do this is to use a well known barrier or effect, but make it actually be something else, like the following trap.
Astral Web (CR 10)
A web fills the hallway.
Type: magical; Perception DC 34; Disable Device 34
Trigger location; Reset None
The web acts like a normal web spell at CL 17 and DC 17. However, the web is anchoring this spot in this plane. If 50% or more of the web is destroyed, the entire area reverts to the astral plane.
A normal course of action here may be to just set the web on fire, and then when a path is clear, move on through. Of course, this course of action will cause the players to end up in the astral plane. The PC’s may think twice when encountering something in the future that appears to have an obvious solution, unless, of course, they really enjoy the astral plane, and they manage to make it back.