There are numerous choices for day trips from Bangkok and, more than likely, your hotel can give you details.Two excellent picks are Ayutthaya and the Ancient City.
Another different kind of trip is Koh Kret
Ayutthaya
Ayuttaya was the capital of Thailand for over 400 years. There are scores of ancient ruins and it is an astonishing place to get pictures of temples and Buddha images. Ayutthaya is only 76 kilometers (about 50 miles) north of Bangkok.
Ancient City
Only about an hour out of Bangkok, the Ancient City is has replicas of many of Thailand's Temples and monuments. It is arranged in the shape of Thailand.
While it may sound highly touristy and Disney like, it actually isn't. The replicas and the spaciousness of the grounds make it extremely realistic, natural and relaxing.
As with Ayutthaya, it is a terrific place for photographers. There are many options for getting around, all very reasonably priced. These include everything from renting a bicycle to hiring a tram complete with guide. The admission fee is 100 baht (US $2.50).
Getting There
For details on getting to Ayutthaya or the Ancient City, talk to the travel agent at your hotel or make arrangements with a taxi driver to take you.
Dealing with touts is not recommended.