happen on/upon something/someone
phrasal verb with happen verb [ I ] uk/ˈhæp.ən/ us/ˈhæp.ən/
literary
偶然发现,偶然遇到
to find or meet something or someone by chance
Eventually they happened on a road leading across the desert. 最后,他们偶然找到了一条穿越沙漠的路。