The Doctor stopped to lock the door, then paused to take in their surroundings.
"Well," said Sarah. "No sign of Daleks, Cybermen, or the Slitheen. This place can't be all bad."
"You know of the Slitheen?" said the Doctor.
"Oh, we've met once or twice," Sarah said.
"Fascinating. You must tell me all about it," said the Doctor.
"Another time, perhaps, Doctor. For now, let's focus on the present, shall we?"
They'd materialized in a meadow, with tall grass and wildflowers. There were woods behind them, and further beyond, hills and mountains. Ahead of them, a river meandered, the water splashing over rocks that jutted above the surface. The air smelled fresh and the sun was warm.
But something didn't seem quite right to Sarah. She knelt down and examined the grass more closely. The ground seemed very dry, and the grass felt brittle. Walking the short distance to the river bank, she saw that the water level had dropped substantially below its normal height.
Turning to the Doctor, Sarah said, "It's lovely here. But they seem to be going through a bit of drought."
"Hmm," said the Doctor. "Do you hear that?"
"I hear something," said Sarah.
"It's coming from that way," said the Doctor, pointing downstream. "Let's see what it is, shall we?"
As they followed the river, the sound became louder, until, after rounding a bend, they found that the source of the sound was in fact a waterfall.
But it was one unlike any Sarah had seen before. Instead of falling over a cliff, the river emptied into a round hole in the ground, an opening some one hundred feet in diameter.
Peering over the edge, Sarah couldn't see the bottom. It went straight down. How deep was it? The wall of the tunnel caught Sarah's eye. It didn't seem to be made of rock or earth. The material was a dark green, with thin veins of gold scattered here and there.
The Doctor lay down beside the opening, opposite to where the river was draining, and let his hand rest on the tunnel wall for several seconds.
"It's organic," the Doctor whispered as he stood up. "The wall of that tunnel is made of living material."
"It's alive?" said Sarah. "But it's huge. It descends as far as the eye can see. And farther."
"Yes," said the Doctor. "Most extraordinary."
The woods came to an end here, and as Sarah and the Doctor turned their attention away from the river, they saw that a footpath led towards a building some half a mile away.
The didn't need to speak. With a shared glance, they tacitly agreed to check it out.
It was six feet in height, hewn from stone, circular in shape, and some twenty feet in diameter. Windowless, there was one door, about five feet high. It was fashioned from some type of earth-coloured resin material, with a metallic area, four inches square, centred about two feet from the ground.
"How very curious," the Doctor remarked as he slowly circled the building.
"Storage shed?" Sarah suggested.
The Doctor stopped at the door and pressed his hand against it. "I shouldn't think so. It's guarded by a rather elaborate mechanism if it is. At any rate, the door's locked."
"Allow me," said Sarah, withdrawing her sonic lipstick from a pocket. She activated it, the lock clicked, and the door swung outward slightly. Winking at the Doctor, who was staring at her wide-eyed, she held it up for him to see.
"Sonic lipstick," she said, then put it back in her pocket.
"Sonic lipstick?" The Doctor said. Then he smiled that broad, toothy smile that Sarah loved. "My, you are full of surprises, aren't you?"
"Just wait," said Sarah. And with that, she crouched down and led the way into the building.
The interior was dimly lit, the light seeming to come from the interior walls, though Sarah couldn't see the source. There was only a stairwell leading down. Sarah descended, followed by the Doctor. The stairwell walls were of stone, but emitted a light that seemed to follow them. When Sarah stopped, the light stopped, and when she resumed, the light continued to accompany them so they could see their way.
They descended for some time in a zigzag pattern, Sarah wasn't sure how far. Eventually, however, they came to the bottom, and found themselves in a huge open area. It was like being in a cathedral, Sarah thought, minus the stained glass windows. Airy, lit with a diffuse light that seemed very much like natural sunlight. Chairs and tables were arranged haphazardly around the floor. One wall was entirely covered in tapestries. Another consisted of a honeycomb of wooden slots, starting from a couple of feet above the floor to some twenty feet high, housing what looked like old, discoloured parchments.
Stepping closer to the tapestries, the Doctor commented, "These tell the story of this civilization. Look. An agrarian people, their dwellings mostly under the ground. There's only natural beauty here. Plants, flowers, rivers, mountains. No scenes of warfare or conflict. But clearly they've also mastered advanced technologies. It seems they've achieved something very few civilizations have: peace and complete harmony with their natural environment."
"No paintings of their people, though." Sarah said. "I wonder what they look like. And where they are."
"This must be a kind of library, or cultural centre, perhaps," said the Doctor, as he walked to the opposite wall. "Possibly their entire history is set out in these manuscripts."
The Doctor and Sarah turned at the sound of a voice.
"You young scallywags!" it said. "How did you get in here?"
"Scallywags?" said the Doctor.
At first all they could see of the newcomer was an earth-coloured, hooded robe. When it reached the bottom of the stairs, a three-fingered hand emerged from the sleeve and pulled back the hood.
It was humanoid, seemingly male, but small, only about three feet tall, with large eyes, a bulbous nose, small mouth, and thick, rust-coloured hair and beard. When he caught sight of Sarah and the Doctor he stopped short, his mouth gaping.
"We didn't mean to intrude," said the Doctor. We're travellers."
"My name is Sarah, and this is the Doctor."
"Travellers," the man repeated weakly. He moved a few steps forward and sat down. "Did you perchance arrive in a blue box?"
"What?" said the Doctor. "How could you have known that?"
Shaking his head, the man stood again, and walked to the wall of parchments, withdrawing one of them.
The man set the parchment down on one of the tables, then rolled it out and held it flat for Sarah and the Doctor to read.
And it shall come to pass that when the river is low, and the grasses are dry, and the crops do wither, that travellers shall arrive, brought forth from a great distance by a box that is blue. And these travellers shall be twice your height, and will be your salvation, for they will cause the waters to flow again and allow all of nature to be healed.
"What are those symbols underneath the text?" Sarah asked.
The Doctor's eyes were fixed on the parchment.
"Doctor?"
The Doctor turned to Sarah. "They're ancient Gallifreyan," he whispered. "Space-time coordinates."