Ayutthaya

Ayutthaya can be seen in a day trip from Bangkok (1.5 hours by train): the ruined Buddhist temples, with the famous Buddha head wrapped in tree roots (Wat Mahathat), are its most iconic image. November-February is the cool, dry season, ideal for exploring the open-air ruins. It's inexpensive, with temple admission much cheaper than in Bangkok. It was the capital of the Kingdom of Siam for over 400 years and one of the largest, most prosperous cities in the world in the 17th century, until it was destroyed by Burmese invaders in 1767, leaving the ruins seen today.