How do i specify a subfolder?

Please pardon my rather stupid question, but I have gone blank. If i want to point my code to a document set under a library, how do I go about doing this? When I point my code to a folder, I do this....

SPFolder mylibrary = properties.Web.Folders["Shared Documents"];

what if I have a document set beneath the "Shared Documents" library, and i want to point to that document set? Thanks