That might be "Side decoration". The side decoration at the tower them is actually in front. ;)

Yup. The side decoration menu is not available in the tower customization menu/

That... shouldnt be. It was at my tower.

It was on mine until I saved the tower style. Then it disappeared.

I think you have to scroll down in the customization menu to see it, which isn't obvious. Took me a while to figure out how to get rid of it myself.