She indicates one of the torches held by rusted wall sconces, taking one in hand. The light plays off the dripping moisture of roughly-hewn walls, although the floor comprises a mix of stone slabs and packed earth. 

Eric does, in fact, mention the glittery outlines of a person they've been following. He rubs his third eye in the middle of its forehead, then checks for confirmation.  

Diana sidles through the tunnel with silent ease. Presto, though, slips on the moist floor and nearly cries out, and Eric tries to catch him and cover his mouth. Unfortunately, that causes Eric to slip, and the two boys go tumbling a short distance, clattering and yelping.  

They've tumbled into a small, half-collapsed chamber, narrowly missing some brackish water. It has flooded half the area, coming from a low tunnel on the far side of the room.    

The rock Eric had placed a hand to lean upon suddenly gives way, falling inward to a smaller tunnel hidden behind. Eric's arm slides easily into the crevice.

ONE MINUTE LATER...

The three move enough debris to reveal a narrow crevice. 

Diana removes her diadem, showing her third eye. The glittering phantoms seem to travel across the brackish water to the west. 

Eric raises his sheild and turns to cram himself into the crawlspace. Diana and Presto shrug, then cram themselves in one by one to follow. 

His attempt at speed belying his attempt at bravado, Eric fails to notice his shield catching at one of the rocky outcroppings, disturbing some rubble and sending a small cascade down on him.

Eric sprawls out at the end of the long passageway, scuffed and bruised. Presto, then Diana, still keeping the torch aloft, step out shortly after, stiff from the close quarters but nonetheless okay.

Diana's torch barely illuminates the passages, with no more wall sconces to help. They turn away from the black water on their left and travel a short way to the right. In the gloom, it seems to end with a dead-end wall, but as the heroes approach, they see an outline of a door with a giant iron ring in its center for a handle. 

From out of Presto's hat swarms a mass of translucent insect-sized wisps, a mass of tiny magical servitors forming a giant hand. It swarms around the door handle and pulls it so violently the entire door explodes inward, sending hunks of stone raining upon the heroes.

The heroes cry out in surprise, but Eric's shield, Diana's grace, and Presto's dumb luck keep them safe from the flying debris.

Eric points to his third eye, then points into the room. The phantom outlines of the man they've been tracking appear again, leaving frame-by-frame after-images of his route.