The following item was purchased on eBay.  It is a "Souvenir Folder of the Pennsylvania State Sanatorium, Cresson, Pa.   It is postmarked Cresson, Pa State Branch, which was the designation of the post office located on the sanatorium grounds.  It was mailed June 9, 1927 to Mrs. C. A. Patterson in Washington, Pa.

 

The item is called a "Postcard Folder", which  is an accordian style postal piece containing a number of postcard views (usually 18) but can be as little as 6 and as many as 30.  The views are printed on both sides of the pages and attached by a fold to each other and to the cover so there are usually half as many pages as there are views.  The folded out views fold together to fit inside a slightly larger cover which has space for a stamp and address on one side and a tab for closing on the other.  The views are roughly postcard size.  The folders were made by the same companies that made postcards of the subject and contain views that can also generally be found on individual postcards.  They have been made since 1907 and are made still today.