They walked a mile or more through the little tunnel. The air was fetid; stale and dank. To Larry it seemed an interminable trip. The narrow passage descended at a constant slope, until Larry estimated that they were well below the depth of the river bed. Within half a mile--before they got under the river--the passage leveled off. It had been fairly straight, but now it became tortuous--a meandering subterranean lane. Other similar tunnels crossed it, branched from it or joined it. Soon, to Larry, it was a labyrinth of passages--a network, here underground. In previous centuries this had been well below the lowest cellar of the mammoth city; these tube-like passages were the city's arteries, the conduits for wires and pipes. It was an underground maze. At each intersection the row of hidden hooded lights terminated, and darkness and several branching trails always lay ahead. But Tina, with a memorized key of the route, always found a new switch to light another short segment of the proper tunnel. It was an eery trip, with the bent, misshapen black-cloaked figure of Tugh stumping ahead, waiting where the lights ended for Tina to lead them further. Larry had long since lost his sense of direction, but presently Tina told him that they were beneath the river. The tunnel widened a little. "We are under the base of the dam," said Tina. Her voice echoed with a sepulchral blur. Ahead, the tramping figure of Tugh seemed a black gnome with a fantastic, monstrous shadow swaying on the tunnel wall and roof. * * * * * Suddenly Tugh stopped. They found him at an arched door. "Do we go in here, or keep on ahead?" he demanded. The tunnel lights ended a short distance ahead. "In here," said Tina. "There are stairs leading upward to the catwalk balcony corridor halfway up the dam. We are not far from the Power House now." They then ascended interminable moldy stone steps spiraling upward in a circular shaft. The murmur of the dam's spillways had been faintly audible, but now it was louder, presently it became a roar. "Which way, Tina? We seem to have reached the top." "Turn left, Tugh." They emerged upon a tiny transverse metal balcony which hung against the southern side of the dam. Overhead to the right towered a great wall of masonry. Beneath was an abyss down to the lower river level where the cascading jets from the overhead spillways arched out over the catwalk and landed far below in a white maelstrom of boiling, bubbling water. The catwalk was wet with spray; lashed by wind currents. "Is it far, Princess? Are those lights ahead at the Power House entrance?" Tugh was shouting back over his shoulder; his words were caught by the roar of the falling water; whipped away by the lashing spray and tumultuous winds. There were lights a hundred feet ahead, marking an entrance to the Power House. The dark end of the structure showed like a great lump on the side of the dam.