Central Thailand, also known as the Central Plains, is the central region of Thailand, by the giant urban agglomeration of Bangkok. Regions Central Thailand can be divided into three regions Bangkok Metropolitan Area Chao Phraya Basin Northern Gulf Coast West of Bangkok

Cities

Ayutthaya - ancient capital built from red brick
Bangkok - Thailand's largest city by far, a sprawling metropolis of wealth,
Hua Hin - Thailand's oldest beach and Resort,
Kanchanaburi - the Bridge over the River Kwai, WWII museums and natural scenery
Lopburi - known for it's Khmer temples and crab-eating macaques
Nakhon Pathom - Thailand's oldest city and site of the world's largest stupa
Nonthaburi - the second largest city of Thailand, actually a suburb of Bangkok
Phetchaburi - known for the Khao Wang mountain and access to national parks
Samut Songkhram - interesting village with the Mae Khlong Market and floating Market

How to get there?

By plane
Most visitors to Thailand will arrive at Suvarnabhumi Airport, Thailand's largest airport 15 km (19 miles) east of Bangkok. It is roughly a 45 minutes ride from The Centre of Bangkok, but heavy congestion could make that trip into 1,5 hours or more. More information about the airport can be found in

By car
The Central Plains has good road connections with the east, south, north and northeast of the country. Two main roads connect the Central Plains with Eastern Thailand. The main road is Sukhumvit Road, also known as Route 3, which starts in Bangkok and via Pattaya reaches all the way to Trat and the Cambodian border. Another route goes east to Aranyaprathet from which the border with Cambodia can be crossed to Siem Reap and Angkor Archaeological Park From Phuket, Krabi Province and other destinations in Southern Thailand, take Route 4 that enters the Central Plains right after Chumphon. Passing Hua Hin, Cha-am and Samut Songkhram, the long ride reaches Bangkok.

Information more at : http://www.tourismthailand.org