Apparently the building that is there today (built after 1903) replaced the original structure that was used as a Confederate Hospital.
"The site’s history dates back to the discovery of deep wells with “healing” water in 1835. A girls’ boarding school opened there in 1854 and the original hotel served as a Confederate hospital after the Battle of Corinth in 1862. A Kentucky soldier left us diary entries of his time there: “April 23, 1862. The [Castalian] Springs are three miles from town [Durant] and the soldiers were brought out in carriages….I am in a room on the second floor, occupied by ‘Morgan’s men,’ the boys I came with, belonging to that ‘layout.’..The building is a two-story frame with ‘wings,’ ‘ells,’ etc. an is accomodating nearly three hundred sick and wounded….nearly all Kentuckians. The grounds are tastefully arranged about the springs, and the scenery in the vicinity is romantic. There was lately a female school kept in this place…..This evening had some pleasant conversation with ladies.”
Forty-three of the soldiers are buried not far from the existing hotel, which replaced the one described above, lost to fire in 1903."
http://daughterofthedelta.com/2011/05/26/spooks-and-spring-water/
Here is the sales listing which includes LOTS of pictures and a layout of the property.
http://www.loopnet.com/Listing/18084324/6786-Castalian-Springs-Road-Durant-MS/