The characters enter a section of corridor, or a room, where roots and vines are growing through the stones. Upon activation of this magical trap, the entire area fills with animated roots covered in long thorns.
Characters must make a Saving Throw vs. Magic, a Dex roll, use acrobatic skills, etc. (GM's choice), or be caught in a sudden briar patch that completely chokes the area. Characters take 1d4 HP of damage immediately, and are completely stuck. Attempting to move, once trapped, proves fruitless, regardless of Strength, and causes an additional 1d4 HP of damage.
Chopping at the roots with swords or axes is of no use, as they grow back instantly, even as they are being attacked. Fire can destroy the thorn patch, but will also burn trapped characters. Magic that controls or communicates with plants might help, otherwise trapped characters aren't going anywhere.
This is a good one for plant or nature-based adventures, when the characters are approaching the final confrontation; it slows them down, and sends the clear signal that things are getting serious.