All your documents are stored on Amazon (AWS) servers based in Australia. Refer also to the FAQ How is our data backed up, how often and how can we retrieve it?
We do not allow you to see the underlying files as this gives you the ability to move documents and cause issues in the database. At any stage, you can always export your documents. Refer to Bulk Export OneDrive.
Note: If you are part of the Beta release for Bulk Export AWS S3, you can also export to a designated AWS S3 directory. Refer to Bulk Export - Beta (this help article is only available to Beta sites).