Seoul sits in a natural basin. Surrounding the city are a number of peaks of 500 meters or more above sea level. These peaks have historically played the role of a natural fortress, providing the city with protection from invasion. In fact, the mountains were a key reason behind the location's selection as the national capital.

Among the major peaks surrounding Seoul are Mt. Bukhansan (Seoul's highest peak at 836m), Mt. Dobongsan (740m), Mt. Inwangsan (338m) and Mt. Gwanaksan (629m). Other peaks include Mt. Bugaksan (342m), the guardian peak protecting the presidential palace of Cheong Wa Dae, and Namsan (232m), which historically guarded the old city of Seoul to the south.

To the west of the city is the Gyeonggi Plain, one of Korea's largest flatland areas and one of the country's most agriculturally productive regions. The Hangang River bisect the city east to west as it flows in a broad "W" pattern. In the old days, the river was home to flourishing river ports at Mapo and Ddukseom and ferry terminals at Noryangjin, Yanghwado, Hannamdo, Songpado and Gwangnaru, but with the development of overland transportation and the construction of large bridges across the river, the city's ports and ferries have disappeared.

Meanwhile, silting along the lower reaches of the Hangang River has created a number of "islands" such as Hajungdo and Jamsil that are now home to massive apartment complexes and residential districts. Another of these islands, Yeouido, has become the Manhattan of Seoul, home to some of the city's tallest skyscrapers, the National Assembly Building and many of the city's major financial institutions.

The Hangang also plays a vital sociological role, separating the city into the Gangbuk (North of the River) area, the older part of Seoul that is home to most of the town's historic neighborhoods and sites as well as its administrative complexes, and the Gangnam (South of the River) area, a recently developed region of relatively affluent neighborhoods that in many ways represent the "Han River Miracle," Korea's dramatically successful post-Korean War economic development.

Besides the Hangang River, Seoul also has a number of large streams that have played a vital role in the city's historic and cultural development. Among these streams are the Cheonggyecheon Stream, the downtown waterway that has recently been restored by the Seoul Metropolitan government to provide Seoul residents with an environmentally friendly recreation spot, and the Jungnangcheon, a tributary of the Han River that’s a popular spot for strolls and relaxation.