Read/Write to folder *above* site root

[Kenny]

I need to read/write .jpg files in a folder *above* the current site's root.
If MapPath is the way to go, then how can I reference the desired folder as
relative to the current site's root (I don't want to hard-code the path from
the C:\root folder.)

For example, suppose I need to write to the WriteHere folder:
C:\SomeFolder\WriteHere

and the site root is MySiteRoot:

C:\SomeFolder\Sites\ASPNet\MySiteRoot

Thanks for helping