Spike Growth

You cause sharp spikes and thorns to sprout in the area, making it difficult terrain. When a creature enters or moves within the area, it takes 2d4 piercing damage for every 5 feet it travels.

Your magic causes the ground to look natural. A creature that can't see the area when the spell is cast can spot the hazardous terrain just before entering it by making a Perception check against your spell save DC.