〜が見える・〜が聞こえる: can be seen; can be heard

Say that something is visible or audible by itself, without anyone trying to see or hear it.

見える and 聞こえる are not potential forms; they are separate verbs and the thing seen or heard takes が. Compare 見られる (can see because circumstances allow) and 聞ける (can hear because you try). Often used for scenery and sounds.