商店街に入ると、陽菜はまるでおのぼりさんのようにキョロキョロ辺りを見回した。

English Translation

As we entered the shopping district Haruna’s gaze darted about, just like she was a rustic from the hills, as she looked over the area.

おのぼりさん or 御上りさん is a little derogatory but common word to refer to a person who comes to/travels around a metropolitan area from a country side. Don’t use 御上りさん if you don’t want to mock the person.
上京する (じょうきょうする) as a verb has a neutral meaning. And 上る (のぼる) = to go up/climb is used both in 御上りさん and 上京する.