Basum Tso (Cuogao Lake) is a high-altitude alpine lake at 3,730 metres, roughly 120 km northwest of Bayi, surrounded by snow peaks and dense pine forest. The water is a deep turquoise that shifts with the light, and the surrounding forest turns vivid amber and red in October. It is one of the most beautiful lakes in Tibet and far less visited than Namtso further west.
In the centre of the lake sits Tashi Island, home to a small monastery decorated with coloured prayer flags. A chain ferry connects the island to the shore in summer. The circuit around the lake takes a full day on foot and passes through some fine forest. Access from Bayi takes about three hours by road; accommodation is available in the village of Gongbujiangda near the lake entrance.