Cotopaxi from the north-west side, run out of working haciendas on the páramo rather than out of a shopfront in Quito. Horse riding across the high grassland, walks to the glacier line, and summit attempts for people who have acclimatised properly.
The office is in Cumbayá, down in the valley below Quito, which tells you the guides are not waiting in the Mariscal for walk-ins. Booking is by email or telephone; they do not advertise a WhatsApp line.