New Living Translation
When you came down long ago, you did awesome deeds beyond our highest expectations. And oh, how the mountains quaked!

American Standard Version
When thou didst terrible things which we looked not for, thou camest down, the mountains quaked at thy presence.

Berean Study Bible
When You did awesome works that we did not expect, You came down, and the mountains trembled at Your presence.

Douay-Rheims Bible
When thou shalt do wonderful things, we shall not bear them: thou didst come down, and at thy presence the mountains melted away.

English Revised Version
When thou didst terrible things which we looked not for, thou camest down, the mountains flowed down at thy presence.

King James Bible
When thou didst terrible things which we looked not for, thou camest down, the mountains flowed down at thy presence.

World English Bible
When you did awesome things which we didn't look for, you came down, the mountains quaked at your presence.

Young's Literal Translation
In Thy doing fearful things -- we expect not, Thou didst come down, From Thy presence did mountains flow.

Isaiah 64:3 Additional Translations ...