Reddit mentions of USB Endoscope 3 in 1 Otg Phone Borescope 5.5 mm Waterproof Inspection Snake Camera Micro USB, Type C for Android Phones, PC, Notebooks, Windows Computer, Mac with 16.4FT Semi-rigid Cord with LED Light

If you're planning on keeping it call a pro or work with it personally over time. Either way get a wire cam from Amazon, drill an easily repaired hole and have a peek inside to see if it's worth the effort.

If you do need an endoscope i really like this $20 i got from amazon..

It comes with a few accesories including a hook which is perfect for dragging rings out of P traps that are set in concrete so you cant open them up.

Its also surprisingly useful been able to see inside the wall when trying to feed wiring down from the attic.

You might want to consider a cheap USB borescope with sticky tape to pull out that Q-tip.

1. Buy a box of commercial ammo.
   
   
2. If it still will not drop into the chamber EASILY, take it to someone with a borescope, or pick one up yourself. They are cheap on amazon. Amazon Link

You could get something like this borescope and drill small holes in the drywall.

Even cheaper and smaller: https://www.amazon.com/Seesi-Endoscope-Waterproof-Inspection-Semi-Rigid/dp/B07PBF6DX5/ref=pd_cp_263_3/145-7175468-0863300?_encoding=UTF8&pd_rd_i=B07PBF6DX5&pd_rd_r=52ad0d7f-e742-4c9f-89b5-03b94a7093c3&pd_rd_w=I7tcc&pd_rd_wg=7Nj4D&pf_rd_p=0e5324e1-c848-4872-bbd5-5be6baedf80e&pf_rd_r=7NNMGR3KX201QB09K1FP&psc=1&refRID=7NNMGR3KX201QB09K1FP

Poke a hole in the ceiling and stick a cheap borescope up there and have a look.

As others have said - it REALLY looks like it's there for a reason. My bet is that it's a sewer cleanout vent... which is there so that a plumber can snake your sewer if there's a blockage before it causes a huge problem. If you're smelling it, it could be the sign of a serious problem- residential sewers should generally not put off a strong sewer smell (generally hydrogen sulfide gas).

If you ARE getting a strong smell, it could be from a few things, including a broken/blocked line somewhere, or even a sewer backup, where something is pushing sewage down INTO your sewer, instead out out from it (this may particularly be the case if you notice the smell after say, heavy rains in the area). Both those problems could be serious, and should be looked into.

I'd talk to a plumber, BUT if you'd rather do that as a last step before trying some things yourself, two suggestions:

1. MAYBE it's some kind of drain and the landscaping isn't what someone thought it'd be. If so, there might be a P-trap of some kind there. A trick an old plumber taught me is to put some olive oil down the drain, which should stop the odor (say, a cup or less should do the trick)
   
2. If you want to troubleshoot a bit, you can get a cheap waterproof(-ish) camera like one of these, roughly $25 off Amazon. It'll connect to a computer or Android phone and let you get some idea of what's underneath there - though obviously you'd want to wash it thoroughly after. You could try that, or even just fish tape, to see if there IS a p-trap of some kind, and see if there's any blockage, or anything else.
   
   If you're really curious and want to make find out definitively what's going on, I'd call a plumber, explain the issue (smell coming from some kind of PVC pipe in your yard), and say you don't know what's going on but you want them to come and scope your sewer. Doing that, they can tell you if there's a blockage, as well as how deep your sewer is and potentially find problems before they become more serious. It might be an easy fix, like snaking the blockage, or the plumber might even tell you you're good to just stuff an appropriately sized rubber ball in the thing and call it a day.