Hearing the sounds of Ca trù for the first time can stop you in your tracks. This ancient sung poetry that's unique to Hanoi has tones that can only be described by the modern ears as otherworldly.

Ca trù dates back more than 1,000 years in history and can only be found in the north of Vietnam. Just like the geisha performances in Japan, this unique musical genre is only sung by women. Barley Norton, who teaches ethnomusicology at Goldsmiths, University of London, believes Ca trù is an "acquired taste, it sounds very alien to people who haven't heard it before." "But once you become acclimatized to the subtleties of the music and the unusual vocal style, it becomes more interesting," Norton told CNN.

The sung poetry is complex in the way that the singer pretty much improvises and "doesn't follow a pulse," added Norton. UNESCO declared in 2009 Ca trù singing as among the "List of Intangible Cultural Heritage in Need of Urgent Safeguarding." Wars and lack of awareness are considered the culprit for the probable demise of Ca trù singing.

Not anyone can sing Ca trù. Bach Van, the 60-year-old performer considered to be among Vietnam's finest Ca trù singers, said it can only be handed down orally from singer to student in a learning process that could take three to 10 years. The trainee also needs to master up to 100 songs before performing to an audience. Van herself claims to have been singing over three decades and only started performing in 1991.

She performs Sunday nights at a courtyard of the historic Dinh Kim Ngan house. The centuries-old venue itself is a part of Vietnam's history as it used to be a communal property. Sadly, Van believes that the culture of Ca trù "will likely die" with her.