Gandharvanagara is a concept found in Hindu books. It is an
imaginary city or mirage town. Hindi Sabdasagara describes Gandharva Nagari as
follows:
Owing to different optical illusions, villages and cities
may appear to exist in the sky and also on seas, rivers, etc. When during
summer the air on the upper strata of deserts, seas etc. gets heated, expanded,
and rises up, the light passing through it becomes multi-coloured and gives
reflections in the sky in the form of village parts or cities. Also can be seen therein reflections
of trees, boats etc. This is a mere optical illusion. This reflection immediately
fades out also. This unreal city, which is an optical illusion, is
Gandharvanagara.
Sage Vyasa in Mahabharata equates Sages disappearing from
sight like the Gandharvanagara fading out.
Gandharva Nagari, an interesting atmospheric phenomenon, is also
mentioned in works on Hindu philosophy — especially the Advaita Vedanta — as an
illustration of something which appears but does not actually exists.
Very rarely this Mirage City is considered as the city of
celestial beings especially Gandharvas.