Options -> Allow Impassible Tiles

The lack of this is a nasty problem, as impassable seems to be filtered out even when selecting "Any" terrain. The result is that searching for Secluded Valley or Sinkhole, etc, always gives an irrelevant error message about caves even though dozens of them meeting the criteria are visible.

Alternatively, remove the options set in impassable terrains, so people don't get confused when it never works. But fixing it to search impassable tiles would be nicer :D