Sultan Mosque, or Masjid Sultan, is Singapore's unofficial national mosque, and it has a peculiarity worth examining.

The black band around the base of its golden dome is studded with glass bottles, most of them old soy sauce containers, donated by those who couldn't afford to give cash when the mosque was rebuilt in the 1920s. The designers thought it right to honour them by working the bottles in.

The original mosque was completed in 1826, a gift from the British to Sultan Hussein Shah. Its replacement, incongruously, was designed by an Irishman named Denis Santry. It is also the only mosque in Singapore permitted to broadcast the call to prayer at full volume across the neighbourhood.

VoiceMap's self-guided audio tours use the mosque as the heart of Kampong Glam, connecting its origins as a Hajj pilgrimage hub to the street art and independent culture that define the neighbourhood today.