Tamul Waterfall is the classic Aquismon excursion and one of the Huasteca Potosina's most dramatic sights. The water drops from the Gallinas River into the Tampaon River canyon, and most visits involve paddling a wooden boat upstream from the Tanchachin side before walking to viewpoints near the falls.
Go with a local operator or boatman rather than trying to improvise the trip. Water levels change the experience a lot: in the right season the river is bright blue-green and calm enough for a beautiful paddle, while heavy rain can make access unsafe.