What is the bottomless pit? In chapter 9 of the revelation we learn that: 


  Revelation 9:1 and 2 NKJV  Then the fifth angel sounded: And I saw a star fallen from heaven to the earth. To him was given the key to the bottomless pit. 2  And he opened the bottomless pit, and smoke arose out of the pit like the smoke of a great furnace. So the sun and the air were darkened because of the smoke of the pit. 


And in verse 11 we find:


  Revelation 9:11 NKJV  And they had as king over them the angel of the bottomless pit, whose name in Hebrew is Abaddon, but in Greek he has the name Apollyon. 


Smith’s Bible dictionary defines the two words as:


  Apollyon
  Apol'lyon. Apollyon or, as it is literally in the margin of the Authorized Version of Rev_9:11, "a destroyer", is the rendering of the Hebrew word, Abaddon, "the angel of the bottomless pit". From the occurrence of the word in Psa_88:11, the rabbins have made Abaddon, the nethermost of the two regions into which they divide the lower world; but that in Rev_9:11, Abaddon is the angel and not the abyss, is perfectly evident in the Greek.
  
  Psa 88:11  Shall Your lovingkindness be declared in the grave? Or Your faithfulness in the place of destruction? 


Psalm 88:11 Westminster Leningrad Codex

הֲלַמֵּתִים תַּעֲשֶׂה־פֶּלֶא אִם־רְפָאִים יָקוּמוּ ׀ יֹודוּךָ סֶּֽלָה׃

According to my Linear translation:

11 [e]

bā•’ă•ḇad•dō•wn.

בָּאֲבַדּֽוֹן׃

in Abaddon

Noun

In Revelation chapter 12 it says:


  Revelation12:7 through 12 NKJV  And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels, 8  And prevailed not; neither was their place found any more in heaven. 9  And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him. 10  And I heard a loud voice saying in heaven, *Now is come salvation, and strength, and the kingdom of our God, and the power of his Christ: for the accuser of our brethren is cast down, which accused them before our God day and night. * 11  And they overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death. 12  Therefore rejoice, ye heavens, and ye that dwell in them. Woe to the inhabiters of the earth and of the sea! for the devil is come down unto you, having great wrath, because he knoweth that he hath but a short time. 


Is there any Doctrine in any denomination which addresses this, since the best I can derive from these passages is that the bottomless pit is a Spiritual prison, in which God has placed Satan and the rebellious Angels.

Chapter 12 of the Revelation has me the most confused, since the indication here; is when this happened, Salvation was set into motion. 

In trying to understand these Scriptures I have concluded that the Revelation Chapter nine, Psalm 88:11 and Revelation 12:7 through 9 are pre Crucifixion while 10 through 12 are at the Crucifixion, especially since:


  Luke 23:44 and 45 NKJV  And it was about the sixth hour, and there was a darkness over all the earth until the ninth hour. 45  And the sun was darkened, and the veil of the temple was rent in the midst. 


Since following the war in Heaven Satan and his Angels were cast into the Earth can the bottomless pit be the Earth as described in Genesis?


  Genesis 1:1 and 2 NKJV  In the beginning God created the heaven and the earth. 2  And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
First, we need to know that Revelation is a prophesy about the future. 


  The Revelation of Jesus Christ, which God gave Him to show His
  servants—things which must shortly take place. And He sent and
  signified it by His angel to His servant John, (Revelation 1:1, NKJV)
  
  After these things I looked, and behold, a door standing open in
  heaven. And the first voice which I heard was like a trumpet speaking
  with me, saying, “Come up here, and I will show you things which must
  take place after this.” (Revelation 4:1, NKJV)


Once that framework is set, we can start thinking from that perspective. The visions saw by John were not related to the past or John's present time. So, the war in Heaven is about the future war between Satan and God and not related to the crucifixion of Christ, and so on.

The Abyss or Bottomless-Pit is mentioned three times in Revelation 9, 11 and 20. Here is a summary of it.


Locusts came out from it (Rev 9)
The Beast ascends out of it (Rev 11:7)
Satan was bound in it for 1000 years (Rev 20:3)


According to Rev 20 (NKJV), the Bottomless-Pit is a Prison.


  1 Then I saw an angel coming down from heaven, having the key to the
  bottomless pit and a great chain in his hand. 2 He laid hold of the
  dragon, that serpent of old, who is the Devil and Satan, and bound him
  for a thousand years; 3 and he cast him into the bottomless pit, and
  shut him up, and set a seal on him, so that he should deceive the
  nations no more till the thousand years were finished. But after these
  things he must be released for a little while. 
  
  7 Now when the thousand years have expired, Satan will be released
  from his prison 8 and will go out to deceive the nations which are in
  the four corners of the earth, Gog and Magog, to gather them together
  to battle, whose number is as the sand of the sea.


The location of this Bottomless-Pit is unknown but it must be somewhere in this vast universe or perhaps out of it, in a spiritual world or whatever you call it. It possibly cannot be on Earth but I can't say it is not. One thing we know for sure is that the Bottomless-Pit is a prison and this is a place where many demons are afraid to go.


  The demons kept begging Jesus not to send them into the bottomless pit. (Luke 8:31,NLT)


Hope this helps.



References:


http://www.biblestudytools.com/dictionary/abyss/
http://www.revelationcommentary.org/09_chapter.html
http://www.greatdreams.com/reptlan/abyss-and-beast.htm
http://www.keyway.ca/htm2003/20030424.htm