Xiyuan Temple is a working Buddhist temple just west of Suzhou's old city, away from the heaviest garden crowds. It has the familiar temple sequence of halls, courtyards, incense, and guardian figures, but the mood is softer than at the headline UNESCO gardens.
The temple is especially good if you want a spiritual counterpoint to Suzhou's scholar-garden elegance. Look for the arhat halls, ponds, and shaded corners where worshippers linger after offering incense. It combines well with nearby Lingering Garden or Hanshan Temple, but is usually calmer than either.