One idea off the top of my head--the temple is scary. Narrow, dark passages, traps, graphic carvings depicting the horrible fate of intruders--*really* scary. Periodic contests to see if the adventurers can overcome their fear and keep going.
Why? Because the temple is actually guarded by fear spirits. If the adventurers figure out that they're under magical attack, they won't have too much trouble driving it off. But unless they've got a skilled spiritist (or better, a shaman) in the group, it may not occur to them that they *are* under attack. They'll just think they're scared.
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