Well here is what we find in Scripture. And of course, it is really beyond human understanding, but it is factual and true.
1 And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand.
2 And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,
3 And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season.
Obviously, since Satan is a spirit being, this "great chain" must be of a very special supernatural construction in order to keep Satan bound. But this is not a "spiritualized" bondage, but a real imprisonment of Satan in the bottomless pit. No matter how difficult it may be for human beings to grasp this and understand the nature of the chain or of the bottomless pit.
But what many Christians have done is simply spiritualized this Millennium and are falsely claiming that Satan is already bound, when the evidence all around us shows the exact opposite. If Satan were well and truly bound there could not be any sin, evil, and wickedness on this earth. So it is DELUSIONAL to make such a preposterous claim when there is no evidence to support it.