It appeared to be a tunnel cut through soft green mould. Its base was a flat strip of pathway a yard wide from which the walls curved out in perfect cylindrical form, smoothed and evened with utmost nicety. Thirty feet wide they were at their widest, then drew toward each other with no break in their symmetry; they did not close. Above was, roughly, a ten-foot rift, ragged edged, through which poured light like that in the heart of pale amber, a buttercup light shot through with curiously evanescent bronze shadows.

“Quick!” commanded Rador, uneasily, and set off at a sharp pace.