RustyC

Ayutthaya is well worth seeing and will keep you occupied for a day. I also once did a daytrip to Hua Hin via rail to check that place out (same way people did 60 years ago).

There's the revolving restaurant at the top of the Grand China hotel in the middle of Chinatown, like something frozen in time from the 60s. Also great views. In the same area on Saturday night is Klong Thom market, where sometimes you see the darndest things in the way of collectible odds and ends. Also not that many farangs (unlike sections of the weekend market).

The Nancy Chandler map has tons of obscure food recommendations, including Kor Phanich (best mango-sticky rice anywhere) and a few places with river overlooks near stops on the water taxi. Bangkok can really reward just wandering around and discovering stuff, especially in the older sections