Once past Phia Den, the road from Cho Ra to Cao Bang climbs for 7km to the Co Lea Pass, crossing part of the large forest which once covered this mountainous region, where the vegetation is made up of an astonishing variety of old trees dotted amid the ferns. At the pass the view of the blue-tinged mountains is magnificent. The road then winds its way down to the vast plain of Nguyen Binh, before climbing up to Cao Bang.