Options for sealing off basement crawlspace

The "crawlspace"

In the back left upper corner of my basement, a hole was made to enable the addition of a powder room on the main floor 15+ years ago. The basement walls are concrete and the hole opening is not smooth nor square. The cavity enabled the installation of a duct, a drain, and cold and hot water lines, and electric.


Additional misc notes

- On the other side of the hole is a cinder-block sided cavern ~10 feet long, ~3 feet deep, ~3 feet wide. (see more pics below)
- I keep a small fan (pictured in the hole entry) on all year long to help air flow.
- I have a dehumidifier in the basement to keep the relative humidity down in the summertime to help prevent prevent mold growth.
- I also run an oransi air cleaner 24/7 about 8 feet from the corner.

The problem

In the winter, cold air sits in the cavern on the other side of the hole and there is a cold draft as a result. In the summertime, this area seems to be more musty smelling and the air coming from the hole seems more humid.





Can I seal it off?

I am looking for advice on how I might seal this off? Specifically, for example, I am wondering if I can seal this off with a vapor barrier and possibly insulation? Or perhaps there is another better approach?