Ancient Portal (Explorers #2)

Story – Part 2: The explorers approached their first discovery, as they did a soft pulsating thrum of a machine could be heard in the distance. At the back of the structure the explorers discovered a giant tunnel with a strange portal at the end – this was the origin of the mechanical thrum that had attracted them. Strange carvings had been made into the entry of the tunnel, seemingly from an intelligent lifeform. A single explorer cautiously approached the portal in the distance.