I'm worried about walking around this area at night.
Literal
Night [at-に] this vicinity [obj-を] walk-[nom-のは] worrying [copula-だ].
心配 ('worry') as a na-adjective — 心配だ ('is worrying, makes one anxious'). この辺 ('this area, this vicinity') is a colloquial spatial demonstrative. を marks 歩く's traversed area.