To Run Parallel To
Godan verb
そう
川の両岸に沿って、ずうっと、美しい桜並木があるんです。
There are beautiful cherry blossom trees all along the river banks.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means run alongside so the verb vocab version is to run alongside.
Think about how you're sewing (そう) something, and your thread has to run alongside the edge of the cloth.