World Heritage: Ayutthaya (2 days and many rolls of film)
On your way back down from the north, swing past this World Heritage Site. Once Thailands capital city in the 14th – 18th Century, it was burnt and pillaged by the Burmese about 400 years ago. You can wander the ruins and climb the temples that still remain today, and take in the morbid beheaded Buddha statues.
Witness the Head of Buddha which is enveloped by twists of tree roots, but be sure to hunch over and not stand higher than its height as a sign of respect. Afterwards, pop into the museum or eat your way through the food market. Personally, I was in rapture when I happened upon the cute and kitsch clothes/accessories market by the Ayutthaya Hotel!