豁然开朗 huòrán-kāilǎng
[the view suddenly cleared up;suddenly see sth. in a clear light] 形容由狭窄幽暗一变为宽阔明亮。比喻顿时通达领悟
初极窄,才通人,复行数十步,豁然开朗。——晋· 陶潜《桃花源记》