山類: sanrui (this is a rather obsolete renku term; the modern term would be simply 山: yama). In traditional Japan mountains hold a special significance. They are homes for powerful gods of Shinto. All major mountains in Japan have shrines and Buddhist temples on their summits or slopes. They are like bridges to the sky, connecting human reality to the divine. The quintessential peak in this sense, of course, is Mount Fuji.
Don't force a Fuji into every renku, though! You can simply use the generic term, "mountain" or, if you feel like naming a particular one, let your imagination rove over the bumpy surface of the planet, at cloud-level. And even if your personal religious beliefs don't include the sanctity of mountains, if you reflect on it, you might find that mountains, for some mysterious and primordial reason unknown to us, fill us with feelings of awe and wonder: an immensity before which we feel like bowing.