Neptune     - the ruler of all water in it's various forms.... 

Neptune's theme is transcendence. He's intense water in a less "physical" mean though - he's about mysticism, spirituality, dreams, ideology but also illusions. He can be blurry, nebulous, veiled... so he's also about "escapism" and therefore told to rule alcohol (beside any other kind of liquid) but any manifestation of "escapism" can be referred to this energy. 
I see him as a "portal planet" and not in the form of "escapism" but in the meaning of finding clarity - to find the own "stream of life", some may call this purpose (a word I don't really like as it's limiting ) but I see it in a more "fluid" way, as to go with the very own flow, integrated, clear knowing and feeling of the inner and outer life and it's connection (also Individual - Collective). Just like a tree - it's roots are as "voluminous" as what you can see above the ground but it's connected through it's form as well as by it's fluids (like blood). 
Further more, when we talk about Neptune and about mysticism and spirituality as well as transcendence there is to note, that he wants to bring us beyond - to see through the sea of emotions to the ground/core. Emotions are actually just a chemical reaction in the body - which serves us very well as inner "communication system" - a biological cellphone that informs us about our "state of mind"....

Greek Mythology:  Neptune (Roman) - Poseidon in Greed - Both the God of the Sea. He's Zeus' Brother and only second in power. His sign is the Trident is seen in all ancient art and is also his astrological glyph - "his animal" is the horse, which he made to give to humanity. As the ruler of all water/liquids, he's a moody deity with a pretty unstable temper but also brave. He preferred to stay on Mount Olympus than his own home down on the ground of the sea. He had a bad relationship with Athena and Odysseus. One of his sons is Pegasus, who was born from Medusa's throat.

Some Astronomy:  Neptune is the eighth and farthest-known planet from the Sun. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, slightly more massive than its near-twin Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. The planet orbits the Sun once every 164.8 years at an average distance of 30.1 AU (4.5 billion km; 2.8 billion mi). The perihelion distance is 29.81 AU; the aphelion distance is 30.33 AU. On 11 July 2011, Neptune completed its first full barycentric orbit since its discovery in 1846, although it did not appear at its exact discovery position in the sky, because Earth was in a different location in its 365.26-day orbit; if the more common heliocentric coordinate system is used, the discovery longitude was reached on 12 July 2011.   (Ref. Wikipedia)    

Below a link to my Blog-Post about Neptune - a "multidimensional" view....

Neptune by NASA and JPL 1998.jpg

Neptune by NASA/JPL (Voyager 2)

Neptune's axis:  (heliocentric)

Southnode: 16°57' Capricorn
Northnode: 16°57' Cancer
Aphelion:     21°47' Virgo     
Perihelion:   21°47' Pisces