Along the Yangtze River
This is a huge river; it is over 6,000 km (nearly 4000 miles) long, about the same as the Mississippi. Only the Amazon and Nile are longer. It is the world's fifth largest river by volume of water discharged, at over 30,000 cubic meters a second, roughly double the Mississippi or Mekong, three times the Saint Lawrence, four times the Danube or Columbia, and more than ten times little streams like the Rhine or Nile.
The Yangtze has been an important transportation route with major cities along its banks for several thousand years.
What we now call Chinese civilization first developed a grain-based agriculture along the Yellow River (Huang He), but different peoples cultivated rice beside the lower Yangtze. These peoples were eventually conquered by Shi Huangdi and assimilated during the Han Dynasty, giving the Chinese (汉人, Hanren) their native name for their ethnicity. Owing to the Yangtze's ease of navigation and much less common floods, as well as millennia of invasion from northern nomads, the shores of the Yangtze became home to many major Chinese cities and numerous capitals, most notably Nanjing.
Many European languages know the river as some variant of "Yangtze" from a poetic name (扬子江, Yangzijiang) for a stretch of the river near Yangzhou. (When Europeans first began trading directly with China, Shanghai was still a backwater and Yangzhou was the major regional port, directing the area's salt trade and commanding the intersection of the Yangtze and the Grand Canal north to Beijing.) Chinese sometimes learn the name as part of their English classes, but Yangzijiang is almost never used in place of Chang Jiang in actual Chinese.
Many of China's greatest cities lie along the Yangtze. Except for Shanghai — which was unimportant until the 19th century China trade made it one of the world's great cities — all of these have existed for millennia. Listed from the mouth up the river, they are:
The river extends far beyond Chongqing; its headwaters are deep in the Tibetan mountains. Few tourists doing the Yangtze route follow the river much beyond Chongqing. However, travelers on the Yunnan tourist trail see some of the upper reaches of the river near Lijiang. The Yangtze is also one of the three rivers in Three Parallel Rivers National Park, a UNESCO World Heritage region in Yunnan.
Several other ancient and important cities are not actually on the Yangtze, but readily accessible from it:
Of course there are dozens of smaller cities as well.
Shanghai has a major international airport with connections to almost anywhere. The other major cities on the route have airports and good connections within China, but not many international flights. However, KLM flies Amsterdam-Chengdu and Amsterdam-Kunming, Lufthansa Frankfurt-Nanjing and Korean Air has flights from Seoul to several of these cities. Finnair  offers direct flights to Chongqing.
From Southeast Asia, the only discount flight into the region is Air Asia Kuala Lumpur to Hangzhou.
The most famous part of this route is the sensational cruise ships through the Three Gorges area between Chongqing and Yichang. With the recent enormous Three Gorges Dam project, this route has changed considerably but it is still definitely worth doing. However be careful of the different types of boats and classes within those boats. Traveling on a Chinese tourist boat in 'first class' may not be your idea of 'first class' (one traveler complained of "rats everywhere"). In addition, the only choice for food may be the boat itself for up to 3-days. As such, bring supplies, particularly snacks and drinks for the voyage. If you really want the good experience on the Yangtze, you'd better choose a luxury yangtze cruise in 4 or 5 star rating. These luxury cruises fare include all the shore excursions with English speaking guides and all meals on-board except the dinner on the check-in day. Almost all the tourists travelling on those cruises are very satisfied with the journey.
While one reviewer suggested not to take the Chinese Tourist boat (since they stop at destinations at 6AM, expecting all passengers to get out and look at the scenery, then arriving at 4AM at the final destination and throwing everybody off the boat), another reviewer had a positive experience despite not speaking any Chinese.
The lower Yangtze areas; from Wuhan down through Nanjing and Suzhou to Shanghai; traveling by boat is also an option, but here it is not essential. There are good rail and road connections throughout the area. See High-speed rail in China for Nanjng-Wuxi-Suzhou-Shanghai-Hangzhou routes.
Be especially wary of thieves on the cruise boats, using any technique from picking pockets to crawling in portholes to rifle luggage.
Chengdu is a hub for visiting southwest China. From there, you can: