Siete Leguas is the traditionalist stop in Atotonilco El Alto's tequila scene. The producer is known for old methods, including crushing cooked agave with a stone tahona, and it has several facilities in town.
Public access is not as straightforward as at heavily touristed distilleries, so contact ahead or work through a guide who knows the Los Altos route. If you can get in, this is one of the better places to understand why highland agave and traditional production still matter.