Sanmenli is one of the quieter components of the Kaiping Diaolou and Villages World Heritage Site. Its great claim is Yinglong Lou, a defensive tower associated with the Ming period and often described as the oldest surviving diaolou in Kaiping. The village setting helps explain why these towers mattered: they were built into farming communities, not displayed as isolated monuments.
Compared with Zili or Majianglong, Sanmenli feels less polished for visitors, which can be a virtue if you have time and transport. Go for the architecture and the rural context, then continue to the better-known clusters to see how later diaolou absorbed overseas Chinese money and Western decorative styles.