The CD12 is a large top-view tube made by the company Rodan-Okaya. 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
Socket type: B12A