At the WBU-ICEVI Conference in Orlando, I got to see a 3D representation of "Washington Crossing the Delaware " created by 3D Photoworks.
Co-founder John Olson showed me that, in addition to being tactile, there are numerous content specific, auditory items embedded in the work that are activated by passing one's hand over them. For example, when exploring the portion of the work that includes horses (background on right), a narrator explains the history of Washington's own horses and their relevance to the war. This was a very cool exhibit.
For more information: 3D Photoworks