Your average dungeon is not just a dungeon. It's also somebody's home or place of work! As such, there should be lots of odds and ends scattered throughout the dungeon. There could be a pile of papers in a corner for no reason. There could be sacks of food left on a table. There may be some statues or paintings placed in a place that makes no sense to you, but perhaps the owner likes to sit there and read or something. There may be tools and other utilitarian devices around that actually serve a purpose - think of your own home and where you've placed your clocks, phones and whatnot. One such device someone may have is a sundial. This is useful to tell time during the day, but what if it also served a dual purpose as a trap?
Sundial (CR 9)
A large sundial sits in the middle of the plaza.
Type: magical; Perception DC 33; Disable Device 33
Trigger location; Reset Auto
When a character's shadow is cast over the sundial, the character is frozen in time, as if affected by a temporal stasis spell at CL 15 with a DC 22 Fortitude save. The character remains in this state until his shadow no longer is cast over the sundial.
I would highly suggest placing this item in the middle of a boss fight against a highly mobile opponent. It should be lots of fun when one of more of the characters gets stuck in time. It will also be fun when the players start asking you questions about the location of the sun in future encounters.