I got this link from a group I subscribe to. 

Quoting the quote..

“”The Stockholm Tunnelbana has three lines encompassing 110km of track and
100 stations of which 64km and 55 stations are underground. Several of
the deep underground stations are cut into solid rock which were left
with cave-like ceilings. The builders carved fascinating artistic
objects out of the rock…”"

Just take a look.  I think its an interesting design, and in any case, it’s a welcomed change from concrete, tile, or fake ceiling material.  You’re in a cave.  Let it look like one.

http://www.techeblog.com/index.php/tech-gadget/
pictures-the-coolest-subway-ever