The area to the left is open terrain, the darker sections are ramps heading down, the rest are caverns.
These long-abandoned tunnels had concealed a House Cannith research laboratory before and during the Last War, and had been overtaken and lost during the magical cataclysm that created the Mournlands. Now, as they investigated, they found a number of hatches at the end of each tunnel. All but one of them were false entrances, trapped with electrical discharges.
The correct hatch was opened with a key provided by their benefactor, and led to a set of rungs descending into the deeps. These led to the Whitehearth Facility.
On their return from the laboratory, the group found Emerald Claw troops with undead support, led by a necromancer and what appeared to be a vampire. An offer to surrender their treasures was met with an open assault, leading to the Emerald Claw troops being routed.