Ochuromaton (trans. "stronghold" and, in the NASB, "fortress") occurs only in 2 Cor. 10:4. The context, though, is ways of thinking. Paul has declared war on mindsets and assumptions. There were those who'd come into Corinth with guns a-blazin' at Paul's teachings. Paul had come back to them, by letter, humbly, admitting that it was easy for him to be bold while absent; but, he admonished them that if it was necessary, he'd come back and be bold face to face, that contrary to all the blistering criticism his opponents had leveled at him after his previous letter to them, he wasn't fighting against the people but was warring for the hearts and minds of those folks at Corinth with the power of thoroughly Godly thinking and wholly Godly instruction.
His thought would be improperly dissected if we take the phrase "pulling down of strong holds" in isolation and then apply it to some mystical battleground to be prayed against, etc. I'm not saying that there isn't spiritual warfare against powers and principalities -- indeed there is. However, this isn't that. This is Paul's direct threat, one that he intends to make good on for the sake of those believers, to put a major quietas on the antichristian critics of Paul, backbiters and false apostles as they were. That's why Paul's whole thought goes into vv. 5-6,
For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds, casting down imaginations, and every high thing that exalteth itself against God, and bringing into captivity every thought to the obedience of Christ; and having in readiness to revenge all disobedience”
This is a very practical instruction to resist those critics to the full and to defend the faith as delivered by him to them, and assurance that Paul himself would do whatever was necessary to make that happen. As I read it, and this is just my own opinion, Paul's use of the word "strong hold" or "fortress" is mocking those critics who think they have got him, think they have a valid wedge against him as they try to get for themselves followers. Compare the power of the gospel and Paul's witness to the power of their rhetoric and their witness.
Human government bears the same relation to hell as the church bears to heaven. (David Lipscomb, On Civil Government, 72).