The Weavemakers hidden threads

The ground in a 20-foot-radius Sphere centered on a point within range conjures several floating golden threads. The area becomes Difficult Terrain for the duration. When a creature moves into or within the area, it takes 2d4 slashing damage for every 5 feet it travels.

As the threads are incredibly thin a target must make a perception check to spot them. Any creature that can’t see the area when the spell is cast must take a Search action and succeed on a Wisdom (Perception or Survival) check against your spell save DC to recognize the terrain as hazardous before entering it.