General facts (From: A.Wildberger, C.Preiswerk, 1997. Karst and Caves of Switzerland). Nidlenloch (SO), located in the Weissenstein, the mountain of Solothurn, was mentioned in the literature for the first time in 1827. The local population certainly knew it for a much longer time. In that year, the alpinist and naturalist Franz Josef Hugi succeeded in progressing 350m into the cave. In 1868, an engineer, Moser, created a 1:1000 scale map and cross-section of the part explored by Hugi. As a result of explorations directed by Franz Held, who organized more then 60 expeditions, at 1909 Nidlenloch reached the depth 396m and became at that time the deepest known cave in the world. Today it remains the deepest cave in the Swiss Jura (418m deep and 7.5km long).
Access. Provided you are in Switzerland take a train or drive to Soloturn (map 1). From Soloturn main station take a local train to Oberdorf (map 2). Then you could either take a walk up the Weissenstein Mountain till the refuge Gasthof Hinter Weissenstein or take a cable car that will eventually drive you up the mountain but not exactly to the refuge. In either way there are plenty of guide signs to find the way. In summer the cable car operates Monday - Thursday from 8:30 to 17:45, Friday - Sunday from 8:00 to 17:45. In winter it works even less time Monday - Thursday from 9:00 to 16:45, Friday - Sunday from 8:00 to 16:45. It is also possible to drive directly to the refuge (except few winter months when the road is closed because of snow). In that case first follow the signs to Langendorf then to the Weissensten. The refuge is actually a farm with a little restaurant and few rooms where one can spend a night. The latter is very useful if you have a long way to Soloturn. To get in the cave one has to take a key in the restaurant for the 5SFr per team plus deposit that will be returned with the key.
Cave description. The entrance is a crack covered with a steel door. It is situated at the South-East side of the mountain Weissenstein, 1274.74m over the sea level, coordinates according to AGN are 603470.4; 233433.6. The steep slope with a stationary rope brings you to the main passage ("Hauptgang"). In about 200m there is a pinch called "Virgin's hole" ("Jungfernschlupf"). That is a narrow flowstone passage approximately 5m long with a diameter going in some places down to 70cm. About 100m further down we pass the small pool proudly named "The Stone Lake" ("Steinsee"). Immediately after there is a passage to the right, which leads to the little system, called "Himmelsgang". After a short rise the ceiling abruptly goes up and the main passage enters a large break. The way further continues down the bottom of the break. After series of easy free 2-3m down climbs the break narrows. The stationary cable rigging that is used only for rescue goes up the crack, but the normal way still continues down the bottom of the passage. There is a crotch approximately 50m after the end of cable rigging. That is the beginning of "Labyrinth" system. The left downward passage goes to the system of the dead-end chambers. The main passage continues if you climb 2m up to the ledge at the right. Taking the passage going further from the ledge you first pass two narrow descending turns to the left and after 15m approach the new crotch. The descending passage to the right is continuation of the main system, the horizontal one to the left is the beginning of the "Truggang" system.
The continuation of the main passage ("Hauptgang"). The way down the main passage is pretty straightforward. The first two obstacles "The Devil's Pitch" ("Teufels-Schaht") and "The Forster Pitch" ("Forster Schaht") are equipped with permanent steel ladders. The bottom of the "Forster Schaht" is the "Forster Hall" where the cascade of pitches "Gressly-Schacht" 13.10m, "Cognac-Schacht" 12.5m, "Nasser-Schacht" <10m?, "Rotschi-Schacht" <10m?, "Gletschertisch-Schacht" 11.3m starts. There are two more pitches on the way down "SAC-Schacht" <10m?, "Biberschaht" <10m?. You do not need a rope to gain further 166m down the bottom of the cave which is the chamber called "The Devils Wall" ("Teufels Wand"), -418m.
The "Truggang-Marchengang" system. First horizontal the passage very soon becomes ascending and brings to the first 7m wall to climb up. There is a permanent aid rope installed. Immediately after there is a second 4m wall which is easy to climb. Further up the passage narrows and after about 70m ends at the head of the first pitch "Narren-Schacht" 10m. You need 15m of rope to rig the pitch using the eyebolts installed. From the bottom of the pitch the passage starts to descend and very soon brings you to the cascade of two pitches "Kanel-Schaht" 10.7m and "Sau-Schacht" 16.3m. Both pitches could be rigged with one 50m rope. Use eyebolts. At the head of "Sau-Schaht" for the sake of rescue operations the permanent traverse line till the first ledge is installed. It is better to ignore the line and make a rebelay directly at the ledge. It is also useful to make a deviation five meters further down the ledge using eyebolt placed. Otherwise on the way up the rope pulls you to the narrow crack. The bottom of the "Sau-Schaht" is a crotch. Standing with your back to the rope passage to the left leads to the continuation of the "Truggang" system, the one to the right starts the "Marchengang" system. First 50m of "Marchengang" are the horizontal crawl that further enlarges and starts to descend. The system ends with a cascade of two pitches "Marchen-Schaht" 12.4m and "Konig-Schaht" 20m. Rig using eyebolts. Through the pinch at the bottom of "Konig-Schaht" one can get to the "Aliengang", "Sandgang" and "Senk-Stollen" systems.
As a supplementary source of information the web page www.nidlenloch.ch could be recommended.
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