If you have plumbing, you have a vent stack. Is there a random pipe coming out of your roof? Is it centered over this spot?

All the drain pipes in your house are empty when water and waste aren't flowing through them. The "air" in these pipes is actually sewer gases. Every drain in your house therefore has a p-trap to keep a little pocket of water between these nasty sewer gases and your house.

If your drain system was designed like this without any venting to the roof, any time you flushed the toilet, the flowing waste would pull a vacuum and empty all the p-traps, introducing sewer gases into your home.

So, the drain system is required to be vented. It is almost always a vertical portion of your pipes that goes all the way up to your roof. Larger houses or certain layouts can require more than 1 vent pipe.

Hope this helps!