Underground Public Latrine Built in 1918 @ Hong Kong

It's just one of the many sloping streets in Hong Kong but this one outside PMQ appeared to have a underground structure by the roadside and this piqued my curiosity.  Looks like a storage room that's locked up although given the wide gap, it's still a bit strange as this would have brought in rainwater and debris brought in by water and wind.  An information panel solved the mystery