how about a weather event? say a sand storm, hurricane, thunderstorm, rainbow without any rain. totem sticks stuck in the ground to mark out ancient hunting territories, a permanent illusion left by some wizard, long forgotten.
a personal favourite: a fairy ring, a ring made of toadstool which supposedly moves anyone standing in it to fairy land. could be an out plane conduit....
for the truly wild: maybe fishes that swim in air...