In the PHOTOS App Preference, where are "Download Originals to this Mac" stored in High Sierra?

I use to store them on an External drive but due to OS issues I did a complete new install after erasing my Macintosh HD and I am piecing everything back together. The good thing is everything is working correctly now.

I have almost 150,000 photos on my iCloud drive with 2 TB of storage and PHOTOS is storing 805 GB of photos and videos there. I just received a warning stating my iMac drive (s) is almost full but it didn't say which drive.

Where are these downloaded Photos stored. It must be originally on my Mac HD somewhere. I am using a 2 TB HD in my iMac, not the original 1 TB.

Thanks

Andy