Mount Inwang (??? Inwangsan), near subway Dongnimmun.
This 336-meter hill is home not only to the eponymous Inwang Temple (Inwangsa), but also Seoul's most famous shamanist shrine Guksadang (???).
To get there, take Exit 2 and start climbing uphill following the "Inwang Temple" signs, through the huge construction site (as of 2006) and up through the temple gate. You'll see a map board and several paths, take the left staircase upward, past the bronze bell of Bongwonsa and you'll reach Guksadang.
Behind it are several creeks with shamanist offerings and the bizarre rock formation known as the Zen Rocks; there are plenty of trails if you want to poke around, and the Seoul fortress wall can be seen running near the top of the hill. Be careful not to photograph or disturb any rituals you see being performed.
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