The terrain is getting higher when you move on from Ning-an Bridge and go west, and all you can see is lofty cliffs and deep gorges. The Central Cross Island Highway was constructed by excavating the marble cliffs, and it was a tough task to build a highway within the precipitous mountains. Peeking into gaps on cliffs from the opposite side, you can see many holes on the limestone walls because of water stream erosion, and thus the grottos were formed, in which swallows built their nests. Hundreds of swallows tweeted, giving this place an extraordinary sight. Also, because Liwu River eroded the gorge, it formed a U shape valley. Several devious tunnels were excavated here during the pavement of Central Cross-Island Highway, and visitors can stroll through the tunnels, look at the stream below the cliffs, and watch packs of swallows at the other end. Standing on this marvelous landscape, you cannot help but admire the profound greatness of nature and manpower. It is a pity that the excessive number of visitors scared the swallows away, and only empty cavities on the cliffs are left for awe.