NET

21 so they themselves can go into the crevices of the rocky cliffs and the openings under the rocky overhangs, trying to escape the dreadful judgment of the Lord and his royal splendor, when he rises up to terrify the earth.

Darby

21 to go into the clefts of the rocks, and into the fissures of the cliffs, from before the terror of Jehovah, and from the glory of his majesty, when he shall arise to terrify the earth.

KJV

21 To go into the clefts of the rocks, and into the tops of the ragged rocks, for fear of the LORD, and for the glory of his majesty, when he ariseth to shake terribly the earth.