Popocatepl & Orizaba
Popocatepetl is a giant strato-volcano whose name means "great smoking mountain" which is apropos since it entered an active period in 2005 can no longer be safely climbed.
Once shrouded in perpetual glaciers around the summit and all along the rim of its giant cone, it now regularly shoots ash and water vapor plumes miles high, followed by super-heated rock fragments. But it was a fun climb while it lasted because it towers over Mexico City and Puebla and the experience of being atop a glaciated volcano so close to 30 million people is quite unique.
El Pico de Orizaba is Popo's neighboring stratovolcano and is slightly taller at 18,491 feet making it the 3rd highest peak in North America. Currently dormant but not extinct, the last eruption took place during the 19th century. It is the second most prominent volcanic peak in the world after Africa's Mount Kilimanjaro.