It is common for flights to circle for 15-30 minutes before being able to land in Vietnam's largest airport.
The alleged shooter in the shocking case, the chief forest ranger in Yen Bai Province, then committed suicide.
Many beams and poles have been damaged by water and the structure has weakened by daily visitors.
Some players have reportedly annotated the Google version of the country's map to aid their quest.
The 45,000 sq.m development will also include walking streets and a square.
Quang Binh Province, where Son Doong Cave is situated, only allows around 600 visitors a year.