Is this just a soffit wall or something else?

We are doing some renovating and I was looking at expanding our bathroom a bit. I pulled the original floor plan on our house trying to figure out what might be in this soffit wall in our master bath but this is all the plan shows:

Attachment 63919

The original owners put the optional bath so we have a shower on the far left and a vanity and toilet on the bottom. Any ideas on what they could be running (if anything) in the X area above the tub? Or why they put something like that in the house in the 1st place? My hope is to just get rid of it. Thanks in advance for any ideas!

Furnace duct would be my first guess.

Nope the return is in the wall on the bottom of the picture there.

Some component of the HVAC, they wouldn't box that out and take up closet space for no reason.

Could be the exhaust stack or vent for the furnace and water heater. Look from the basement.

Look up on the roof above that area. If the furnace vent runs through that box it will show up directly above on the roof as an 8" pipe with a cap.

http://t.harborfreight.com/digital-i...era-62359.html

Pencil size hole, probably $72 with a coupon