Ulsan, like any city in South Korea, is relatively safe by global standards.
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The primary language of Ulsan is Korean. English is not common especially among the older generations and many younger Koreans are shy about using their language skills. They'll often nod and say yes without really having understood a question - which can lead to problems when asking for directions. The Korean phrasebook should provide some useful words and expressions.
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Official English-Language Website for Foreigners in Ulsan (http://ulsanonline.com/). Read up on the goings on in Ulsan and share with other expats.