Volcan Copiapó (6052m) is probably the easiest (from a technical perspective) and most accessible 6000m peak in the Puna de Atacama, if not the world. This makes it super runnable and a great training peak for other 6000m mountains and a good place to practice moving quick at high altitude.

The trail head is reached via mining access roads and you'll probably want a high clearance vehicle to get there.

This is THE classic climb in Quito, Ecuador and is a route where all of Ecuador's best trail/mountain runners have trained and put up times (as well as many foreigners).

Note that there are many routes up Rucu, but this is the most competitive. The other route-variation considered for FKT purposes will be the Polichaski ascent, starting from the sidewalk at Bosque Miraflores.

This route starts from the entryway to the Teleferiqo ticket-office and finishes at the summit