Niujie Mosque solved the problem of a minaret without building one that looked like a minaret. Rather than the tall cylindrical tower familiar from mosques in the Middle East or South Asia, the mosque's call to prayer historically centered on the Bangke Tower, a two story wooden structure in the courtyard built during the Song dynasty as a depository for scripture before later serving as a calling tower, rebuilt in its present form in 1496 under the Ming dynasty after earlier structures were lost. Its outward shape, tiered eaves and a hexagonal plan, reads as Chinese religious architecture in miniature rather than announcing itself as Islamic at all.
A second and more distinctive structure serves a purpose unique to Niujie among Chinese mosque architecture. The Wangyuelou, or Moon Watching Tower, a hexagonal, double eaved pavilion glazed in colored tile, stands at the mosque's southern edge for a specifically calendrical function: each year, in the ninth month of the Islamic lunar calendar, the mosque's imams climb it to observe the moon directly and determine the start and end of Ramadan by sight, continuing a method of lunar observation predating any telescope or printed calendar the mosque might otherwise have relied on.
Both structures sit inside the same Chinese courtyard vocabulary that shapes the rest of the complex, painted timber brackets, upturned eaves, a central axis, applied here to functions no Chinese temple ever needed: sighting a new moon, and calling a Hui congregation to prayer five times a day for roughly a thousand years.