Dai Yem Waterfall is the classic Moc Chau sight: a broad cascade outside town, reached by a short path and best after rain. The falls are not remote, and local tourism infrastructure has grown around them, but the water, greenery, and cool air still make the stop worthwhile.
Go early if you want photographs without crowds. In the dry season the flow can be modest; in the wet season the falls are stronger, but paths may be slick and the spray heavier.