Thonburi was briefly the capital of Siam after the sack of Ayutthaya in 1767. However, King Taksin established his new capital Krung Thep (the Thai name for Bangkok) on the east side of the river in 1782, and Thonburi has been a little behind the times ever since.
An extension of the Skytrain across to Thonburi is half-complete, but caught in political squabbles and unlikely to open before 2006 at the earliest.
There are two train stations in Thonburi, both comparatively quiet.
The Chao Phraya River Express stops at a few points on the Thonburi side, notably at Wat Arun and near the old Thonburi railway station.
The Southern Bus Terminal (sathanii sai tai mai) is on Boromratchchonnani Rd in northern Thonburi. Long-distance buses leave from here to destinations throughout western (Nakhon Pathom, Kanchanaburi) and southern (Krabi, Phuket, Surat Thani, Hat Yai) Thailand.
Unless you want to brave the local bus system, the only practical means of reaching the terminal is by taxi.
Thonburi's top sight is the Temple of Dawn (Wat Arun), usually covered by a short ferry hop from the Rattanakosin side and hence covered in the Rattanakosin article.