How do I grant read access to just one specific folder?

I was asked to grant a read-only access to contents in a single folder (and its sub-folders), within a product context to which this particular user does usually have access (they're not part of any team that has access to this product context).

Is that feasible?  And if so, how do I go about doing this?

I tried to use the "manage security" function and have granted "Read" access to this user / group, but now I don't know how they can navigate to this folder and add objects to their workspace etc...  - in other words, the product context does not show up in their list of places to browse...