There were six of the openings, each one leading into unknown depths.

They were only a meter apart, but in every other respect there lay between them a gulf of unknown depth.

At the end of the hall the floor vanished and fell to an unknown depth.

Some strength rose up from unknown depths in Kirk.

In contrast to the teleportation down into an unknown depth the jump to the surface was child's play.

Whoever tried to cross would immediately sink to an unknown depth.

He saw steps leading down in a broad sweep from the street into unknown depths.

His mind told him that at any moment he was going to start plummeting to some great unknown depth.

The set went clattering out of sight into unknown depths below.

Every few seconds, a thin illuminated red line marking some unknown depth passed.