More Space Unavailable than used

I fresh installed windows 10 about a two weeks ago.  My computer says that I have used 264GB of space. 

My C drive (the only partition that I know of) contains the following folders:

Identity            0
Intel            510 kb
Perflogs        0
Program files        1 GB
Program Files x86    19.3 GB
System.sav        1.5 MB
Users             19.3 Gb
Windows        15 GB
Windows Old        3.03 MB

Total = 55 GB

It lists desktop, music, pics, docs, videos and downloads at the same level as C but I think these are all actually contained in users and are no more than 20 GB in any case.

Where are the other 209 GB of used space and how do I get them back?