Ayutthaya

Most visitors get out the way they came — from Bangkok. But there are a number of other interesting next stops in the area:

Bang Pa-In — famous for its eccentric palace and only 20 km to the south

Kanchanaburi — the famous Bridge over the River Kwai and numerous World War II museums

Khao Yai National Park — first and largest national park of the country

Lopburi — the next destination if you take the train north, with monkeys and ancient ruins

Nakhon Ratchasima — gateway to the Isaan region

Sukhothai — another former capital of Siam with impressive ancient ruins