"I know," I said humbly.
"Hasten, Andvar!" called the other Alfings softly. "The Jotuns may come at any moment."
Andvar heeded their anxious warning, and hurried through the crevice by which we had just come. The thump of their heavy tread died away.
"Can the Jotuns get to Loki's prison without going through Alfheim as we did?" I asked Frey.
"Yes. There are many ways from the surface into these caves, Jarl Keith. The Jotuns will come by one of them."
Holding the torch high, I advanced with Frey through the lofty cavern. A profound silence made the guttering of the torch, even my own breathing, seem loud to my ears.
My heart was pounding as we approached the shimmering door at the end of the cavern. Now I saw that the door was not of matter at all, but of force, that apparently their web of light was probably less vulnerable than any material door could be. It was projected from apertures on either side of the opening. I guessed that hidden inside the rock must be the mechanisms that projected the force. Frey confirmed my guess.
"Odin himself devised the projectors and sunk them in the rock. They are operated by inexhaustible atomic power, and generate an absolute barrier to all three-dimensional matter. They are controlled by the tiny projector in the rune key. That is why, if the key were destroyed, the door would vanish in one terrific flash of force."
With a queer, shrinking dread, I approached the transparent web. I was about to touch it when Frey hastily drew me back.
"Keep a safe distance," he warned. "The extra-dimensional force web would blast your hand."