This is a post without pictures. I only can refer you to above video on Daily Motion, a 11.05 min video entitled La grotte à Maurice, made by Julien Maguin and Philip Lespinasse, intended as a documentary on an aspect of outsider art.
Maurice Dumoulin (1907-?) from Switzerland is the leading character of the movie. He was filmed when he was almost 100 years old, and revisited a grotto he had digged out himself. According to the Lausanne Art Brut Museum he has been active in digging the grotto from 1975 till 1995, according to a regional newspaper (meanwhile no longer available) he has done this from 1978 till 1984.
Anyhow, digging out the grotto has been an enormeous project. The grotto, in the woods near Bussy, a small community in the canton of Fribourg in Switzerland, is 16.5 m long, 2 m wide and about 2 m high, which means that he must have removed singlehandedly and with simple tools some 60 cubic meters of rubble.
Dumoulin has redefined this grotto into kind of an outsider environment by filling it up with an altar and a huge collection of all kind of objects he brought there, bottles, newspapers, ceramics, iron utensils, objets trouvés one could say, stuff that should have been discarded from another point of view.
I am not sure if there are any creative aspects in this collection of objects. On the internet I could not trace evaluative descriptions, and Dumoulin, as seen and talking in the film is probably too old to be coherent in explaining what this is all about.
As far as I understand the shots of Dumoulin revisiting his grotto have been done in the autumn of 2005; the film has been edited in 2008.
The movie was part of an exposition in the Collection d'Art Brut in Lausanne entitled l'Art Brut Fribourgeois (febr-oct 2009), curated by Lucienne Peiry, at that time the director of the museum.
So, with this imprimatur I suppose this grotto should be ranked as one of Switzerland's outsider environments.
On Google Books parts of the publication coming with the exposition have been republished (with pictures by Mario del Curto of Dumoulin and the grotto)
first published may 2010, revised aug 2012, feb 2015
La grotte á Maurice
Woods of Bussy, CH