The CD12 is a large end-view nixie tube made by the Rodan-Okaya of Japan. Rodan are known for making the largest (and some of the strangest looking) nixie tubes in the world.
Here are some photographs of the tube from various angles, followed by a video of it in action. The datasheet is at the end.
This is an excerpt from a catalog at Dieter’s excellent web site.CD-12 data