I found where Media Creation Tool saves downloaded files, a folder with a size of some GiB, it is:
C:\ESD\
I found that by reading the file:
C:\$Windows.~WS\Sources\Panther\setupact.log
There are lines with:
Transfer progress: [0%]
Transfer progress: [1%]
Before that lines (a few lines before them) there are lines with the text:
SetupManager: X86 Url =
DlpTask: Adding file: Name = [], Source =
SetupManager: X64 Url =
DlpTask: Adding file: Name = [], Source =
And on the end of that lines, there is the destination folder:
, Target=[C:\ESD\Download\installx86.esd]
, Target = [C:\ESD\Download\installx86.esd]
, Target=[C:\ESD\Download\installx64.esd]
, Target = [C:\ESD\Download\installx64.esd]
So i checked C:\ESD
size and it grows as download progress.
Media Creation Tool also create two folders (a few MiB in size):
C:\$WINDOWS.~BT
C:\$Windows.~WS
Hope this helps!