Sotano de las Huahuas is a deep karst sinkhole near San Isidro Tampaxal, best visited around dawn or dusk when parrots and swifts move in and out of the void. It is less famous than the nearby Cave of Swallows, but it has the same powerful combination of birds, forest, and empty air under your feet.
The approach is on foot through the community area, with steps and uneven paths. Bring a lamp for very early starts, keep well back from the rim, and take local advice seriously; this is a natural abyss, not a fenced city lookout.