Synesthesia is a very compelling phenomenon to study, mainly because there is no outright explanation for it. I also find it particularly interesting because I experience spatial sequence synesthesia. Numbers or dates (in my case) seem to float around in space. I can sense the presence of representations of days of the week, but I can’t fully visualize them. They may appear in boxes, closer or further away from each other, or they may just hang in the air. Many times, I’ll “feel” a black background which helps each day, outlined in white, stand out, just as if I was thinking of a calendar with my eyes closed.
Interestingly, this specific type of synesthesia is thought to be linked to superior memory. I cannot vouch for that myself, as I have a terrible memory, but many people experiencing this can recall memories to an incredible level of detail.
I also found this interesting short film that artistically represents synesthesia of sound, color, and taste. I encourage everyone to check it out!
http://www.youtube.com/watch?v=aIEiOrxhtNQ