The Gnomes have indeed broken into something ancient. The floor is collapsed and below it is a pile of rubble with a passage leading off. There is the persistent sssh sssh sssh sounding like whispers, it is louder from below, but still could just be tricks of wind across something. The passage is 20 feet wide and domes to a 20 foot high ceiling.
The walls bear simple geometric designs, elongated lines and shapes that snake in various directions. They once look to have been painted In colors purples and yellows, but the paint has flaked off. Some of the lines have as well broken away from the walls, heaps of plaster line the corridor.
There are some ropes attached as if someone had lowered themselves in here. Away from the pile of rubble you see several sets of footprints leading inward. 50 feet in the corridor comes to a 4 way. To the left and right are large alcoves, 20 feet wide and 30 feet deep. . the several footprints lead around in here as if this area has been investigated. To the right is a long dry bedroll, hardened to almost petrification by age.
Ahead you think there is a faint flickering light.
The corridor continues another 50 feet and 4 ways again. To the left and right are longer alcoves, still 20 feet wide but now 40 feet deep. The one of the left holds what looks like a smashed picture or mirror frame. To the right the end of the passage has collapsed. The frame looks to have once held a mirror, full length dressing mirror. There looks to be no shattered glass and only 1/3 of the frame remains. A careful inspection turns up what look like glass, possibly very highly polished stone., only a few small shards though.Ahead you now are sure you see a faint flickering light.
50 feet on and the corridor 4 ways again. This time a huge octagonal room 50×50 with 30 foot wide corridors going off in 4 directions and a 30 foot high domed ceiling. . Ahead is seemingly a wall of spider webs, behind it a flickering green light. There is the faint smell of decay in the air. As the other 4 ways the left and right end in alcoves.
There are footprints and drag marks leading to the right, and footprints turning and running from this area. the whispers you have heard increase, echoing in this larger chamber.
To the right are two piles of rubble, the ceiling has partially collapsed, the drag marks and footprints go behind the rubble. To the left 3 short stairs lead to a marble dais. There is a fresco scene painted on the wall, a shout comes from behind you. Turning 3 ghouls emerge from rubble.
The Ghouls rush the party, Helm uses his holy symbol and turns them. Ones runs into the spider webs and the other 2 flee back toward the rubble. Melee weapon and spells cut down the fleeing ghouls, one manages to pull apart a lot of spider web. You see a multitude of small black spiders coursing across its body. In the hole it made you can see stairs descending.