what you said upstairs is correct, that is, if you leave Jiangnan Park and go to Longtan Mountain, you should take the No.3 bus without passing by the river, but I suggest you take the No.42 bus along the river to enjoy the scenery.

get off at jiangbei station, but it's relatively close to Longtan mountain. it costs no more than seven or eight yuan to take a taxi, so you can stay in jiangbei. Tianjin street will be far from your station, opposite which is Jilin institute of chemical technology, and there must be many hotels around.