Here is another installment of exTRAPaganza, our Thursday over-the-top trap series.
The huge wall has scaffolding on the outside.
The scaffolding is not balanced and collapses when a target reaches the upper levels. This also takes out the wall.
This happens about 100 feet up. When the scaffolding collapses, all targets may make an average Dexterity saving throw to jump, taking the appropraite falling damage. Otherwise, they take massive bludgeoning damage as the scaffolding and wall collapses on top of them.