The 200-ft-high Gilbert Hill faces threat from haphazard real estate growth around it. Pic/ Sayyed Sameer Abedi

Tucked inside the concrete maze of Andheri West is Mumbai's -- nay India's -- best-kept 'secret': a 66-million-year-old volcanic structure that can be found at only two other locations in the world. And, a filmmaker from Delhi is outing it. Jaskunwar Kohli, 24, who studied filmmaking at St Xavier's College two years ago, has released a short film -- Nobody Knows -- on YouTube that throws light on 200-ft-high Gilbert Hill, a volcanic structure from the Mesozoic era believed to have been formed at the time of the mass extinction of dinosaurs due to an asteroid hit.