That done, Childermass starts that way, walking towards the stairs. As he goes, however, he does continue talking.

"Good. See if you can find anything else down here," he says, then adds, again to Taako, "Including you. You may as well try knocking on everything as long as you're the Prince."

Seriously, just start knocking on everything, people. He's running out of ideas here save for getting a look at the sun crystal up above.