The Gopher Bridge caves are approached by two openings, one known as the Old Entrance, the other as the New Entrance. Mr. Wheeler used the former in his visit, and took his observation by the light of gas lamps and magnesium wire. Not far from the entrance he came to a place where the passage dropped suddenly into space. "Standing on a ledge that overhangs a black abyss," he says, "the eye is first drawn by a subterranean waterfall heard roaring immediately on the left. It appears to pour from a dark opening above it. Below, between black walls of rock, may be seen the foam-flecked torrent hurtling down the incline until lost in dense shadows. Overhead, fantastic spurs and shapes reach out into the blackness, and the entire surroundings are so weird and uncanny that it is easy to imagine Dante seated upon one of these spurs deriving impressions for his Inferno. As the brilliant light gives out, the thick darkness makes itself felt, and instinctively you feel to see if Charon is not standing beside you. This subterranean stream with its unearthly surroundings is suggestive of the Styx and incidentally supplied the name Avernus for the cavern of the waterfall." The Cavern of Avernus is reached by the New Entrance, through a small passage. Cougar Brook emerges from the Gopher Bridge caves 450 feet down the valley, and after pouring down a rock-cut known as the Flume, disappears into the Mill Bridge caves. The entrance is some thirty feet to the east, through a cleft in the rock. A passageway of 400 feet leads to an irregularly shaped chamber known as the Auditorium, through which Cougar Brook roars its way. "Faint daylight enters through the passageway of the waters, making the place look dim and mysterious." The passageway is broken at intervals by potholes, ten or fifteen feet deep, necessitating a series of rough ladders, and in one case a floating bridge as the pothole is half filled with water. Emerging from the Mill Bridge caves, the brook runs for 300 feet through a deep gorge spanned by two natural bridges, and then enters the third series of caves. Creeping down a long passageway, with the dull roar of the stream ever in your ears, you come to a sharp descent of twelve feet with natural footholds, but persons unaccustomed to climbing are advised to use a rope to steady the descent. "Here the brook is heard far down rushing through some rock-cut with a dull intermittent pounding like the blows of a giant sledge-hammer." A passage to the right brings you to the Dropping Cave, with walls and ceiling of dark blue limestone streaked with white calcite, and water dropping everywhere from the roof. From the eastern end of this cave a narrow passage leads to the Witch's Ball Room, a triangular cavern whose floor is broken by deep cracks "leading down to where the underground stream roars threateningly." Beyond this are several other passages and smaller chambers, the farthest known as the Pit.