i particularly like the stockholm metro stations. more specifically the exposed bedrock, tho I'm not a huge fan of the painting over of it. my hope is that when (if) relief line is built we can get some exposed bedrock sections. i know our shale bedrock is flaky and fragile closer to the surface, also that it has a tendency to expand when exposed to air/moisture. but if it was at all possible, or if it were to be covered with transparent glass/plastic, i think it'd a great for the public to see in some stations. wouldn't have the greatest hue compared with some bedrocks (e.g red granite), but it's made up of a series varved layers laid down annually ~400m years ago. with the right lighting these contrasting lines can look pretty nice.