Drain mystery - What is it?

[clunky]

I'm starting to remodel a basement bathroom. After removing the old sink and vanity, I discovered this drain access/opening (see photo) that was hidden under the cabinet. What is it? Was a toilet located here sometime in the past? Actually, I wouldn't mind locating the new toilet here, if that's what it is.

Thanks for your advice!

 

[Mr_David]

Probably just a clean-out. That brass plug can be very hard to remove. Most likely you will have to cut the plug out. Replace it with a plastic PVC or ABS plug