One of the most distinctive buildings in central Seoul is the 33-story Jongno Tower, a triangular glass and steel tower topped with an oval floating above seven stories of emptiness.
Across the street is the traditionally reconstructed "Bo-shin-gahk" belfry, housing a large bronze bell. During the Joseon dynasty, the bell would be rung 33 times every morning, (symbolizing the 33 heavens of Buddhism), to open the city's gates. At dusk, the bell would be rung 28 times (linked to the locations of constellations) to signal the shutting of the city's gates.
The original bell is now in the National Museum, but a reproduction still hangs here, and every December 31, it's struck 33 times to ring in the New Year.
The basement of the Jongno Tower connects with the subway and a shopping arcade, including "Bandi and Luni's," one of Seoul's largest bookstores, with a good selection of English publications. While there is no public observation deck at the top, there is a restaurant/bar, and if you take the elevator to the top, you can linger for a few minutes in the foyer area to catch a view without having to buy anything.
(Incidentally, Jongno Street, one of the city's main east-west thoroughfares, means "Bell Street." The bell's been ringing here since the end of the 14th century.)
To get here by subway: Take Line 1, exit Jonggak station.
More info about the architect, Uruguayan Rafael Viñoly, and the architecture: http://www.rvapc.com/works/341-samsung-jong-ro-tower