A deep, muffled rumble echoed from the direction of the crevices they'd just passed. The ground trembled slightly, sending fragments of stone down.

"What is going on?" the guard captain cried out, his voice tinged with alarm as he stared toward the entrance.

The entrance, which had allowed only one person to pass at a time, was now completely blocked. An enormous boulder had appeared there at some point, and no one had noticed it. It was as if an invisible giant hand had sealed off their escape route from the outside.

"Damn it! Our way back is cut off."

One guard rushed forward and shoved against the massive stone with all his strength, only to find it immovable. It was heavier than he could have ever imagined.

Panic spread as the others rushed forward, hacking at it with swords and axes. They managed only a few white scratches on the boulder's surface. It didn't look like any ordinary rock and seemed to be bound by some kind of restriction seal.

"It's a formation! We're trapped