What happens to the 3 cards that are turned up when claiming a tunnel on the Switzerland map? Are they placed back on top of the draw pile or are they placed at the bottom of the draw pile or are they discarded?
There's no information in the rules about it.
They're discarded.
From the Switzerland rules, page 2:
The three Train Car cards revealed for the Tunnel are discarded.
Note that train cards are never put on the bottom of the draw pile. Only when the draw pile is empty does the discard get shuffled to replace it.
