First, a couple of minor corrections. Due to my near-total lack of German vocabulary, I had been lead to believe that the venue was some sort of disused mine. It is, in fact, a tunnel bored into the side of the mountain by the Swiss Strategic Security Institute. While there was a restaurant and several temporary bars and rest areas in the space we could get to, the large maps also clearly indicated a heavy weapons testing range in one of the restricted sections. So "disused" isn't even close - this is an actively maintained facility.
The tunnels were all decorated with excellently placed lights and large amounts of construction equipment.
Finally, the shows themselves were excellent. Covenant and VNV Nation both played great sets; the crowd was very high-energy and both acts responded to that.
Discussing it with my traveling companion, we agreed that even if it had just been a club night in the venue, it would have been superlative. After Covenant's set, I could have gone home happy. By the end of VNV's set, I was ecstatic.
Uncharacteristically, I took about 200 pictures of the hole thing, lots of which are blurred to hell.
As hoped, it serves as a nice coda to my trip. Tonight I stay in, tomorrow is a day at work, and I return home Tuesday.