No one has actually seen it, but a fairy interpreter asked a fairy and they described it as just a cloud of smoke and once in a while you trip over something in the floor.  The fairies purposely leave their trash in the floor because they think it is funny when people trip over them.
Inside the fairies church, Inside Church
fairy interpreter
fairy
I'm a fairy that lives in the forest. I like to fly around with my siblings and play games. I try to hide from humans. If they find me, I'll grant their wishes.
Tee hee. You speak so fancily. Who do you want me to speak to? Oh! Sorry, I've never been in a fairy church before. Can hardly see you around all the smoke. Could I ask you for a wish? Of course you can ask, and I will do my best to help you, but only one time, so wish carefully. My mom's got the cancer. My dad's got coal lung. My sisters are starving in the streets. Could you make me a mega-millionare? If that is what you wish, then that is exactly what I will do.  What? Just like that? No blood rites? I didn'- Don't even have to kill my parents? Don't be silly. I am happy to help. Just go back on the path you came here and turn left towards the shoreline. When you get to the water look down. You will see mega millions of grains of sand. And they are yours. You are a mega millionaire! Ah, good joke. Anyway, let's talk money. Could I have an insane amount of it? Sorry, only one wish. I'm pretty sure I mentioned that to you. Those are the rules in the Fairy Church. I never said that was my wish. Well, you can always take me to fairy court. No, it's no bother good fairy. I'll find someone else. That being said, do you need any help? 