The noise of the rain echoed off the old stone walls of the market square. Simon, Lena, Filip and Ola crowded under the canopy of an antique shop, waiting for the downpour to pass. They had walked these streets so many times, but tonight everything seemed different - as if the city breathed deeper, whispered something in the darkness. Simon glanced at his watch. "Last bus in half an hour. Before we go through the market, why don't we see that well again? Who locked it up with four triggers anyway?" Ola rolled her eyes, but didn't say no. They were all afraid of this well, since the older boys had told them about ghosts and the dragon under the town. So all four of them moved towards the old iron railings flanking the centuries-old manhole. That evening the manhole was open. A rusty padlock lay abandoned on the cobblestones, as if someone had given up in a hurry to close the passage. Lena bit her lip and chuckled quietly: "That's strange... It was always locked." Philip illuminated the entrance with the torch from his phone. There was a chill from the darkness, a smell of wet earth and something unfamiliar, as if there were metallic notes coming from underneath. For a while no one moved. "Are we coming down?" - Simon asked, trying to sound brave. Ola nodded, and Lena was already the first to put her hand on the ladder. One by one they went down, feeling the sounds of the city closing over them and the darkness thickening around them. After a few metres they found themselves in a wide, arched tunnel. The walls glistened with dampness and were full of mysterious scratches - as if someone had hurriedly left marks here in the past. Philip brightened the light a little and then they saw what was at the end of the corridor: a steel door with the date "1424" and a strange triangular symbol engraved on it. The door was a millimetre wide open, and from behind it came a quiet, steady sound - pulsating like a heartbeat. Lena chuckled in a whisper: "I think it's the beating of.... just what?" Suddenly, as Lena reached out to touch the door, there was a creaking sound in the tunnel, and just behind them, someone hissed: "Don't come in..."