5. Sonbhandar Caves, Bihar
Sonbhandar Caves are two rather strange cave chambers in Rajgir, Bihar that are hollowed out of a single massive rock.
It is estimated to date back to at least 3rd – 4th century AD by the inscriptions in the western cave.
The western chambers are believed to have been the guard room and the doorway is supposed to lead to King Bimbisara's Treasury.
Inscriptions in the Sankhlipi script, etched into wall of the western cave and so far undeciphered, are believed to give the clue to open the doorway.
The treasure, according to folklore, is still intact.
The mark on the supposed doorway where the British tried to cannon ball (without success) their way through can still is seen.