When Zuko touches the crystal, it shines brightly, turning the usual blue. The gates at the end of the walkway open up, the bars disappearing into the edges of the gate, allowing everyone to walk by. From the chamber Zuko is in, a stair emerges from the bottom edge of the cube, allowing for a safe descent onto the walkway.

A rousing success, everyone! In...some way. As they say, no pain, no gain, right?