Type of Object That May Meet an Unstoppable Force

This page is the CodyCross answer for the clue below from Making a Documentary, Group 1511, Puzzle 1 (Unsolved Mysteries).

Question is: Type of Object That May Meet an Unstoppable Force

and the answer is: IMMOVABLE

Word Meaning:

IMMOVABLE — incapable of being physically moved; fixed

Definitions from Wiktionary.