Twenty-five kilometres east of Riobamba, EL ALTAR (5320m) is an extinct, heavily eroded volcano rising to the south of Volcán Tungurahua. Named Cupac Urcu, or “sublime mountain”, in Quichua, El Altar boasts a breathtaking crater set within an amphitheatre of jagged, ice-capped peaks studded with hanging glaciers that are constantly rumbling and cracking. The principal of the volcano’s nine craggy summits is El Obispo, a difficult technical climb not conquered until 1963 and best left to experienced mountaineers. Lying in the bottom of the crater is Laguna Amarilla (4300m), whose yellow-green waters are dotted with blocks of ice that have calved off the glaciers above. A wide gap in the west side of the crater opens onto a flat plain known as the Valle de Collanes, providing easy access down to the lake.