This was a fun one. I had built a niche into the wall of my bathroom remodel with the intent to install shelves. I didn't want the traditional wooden blocks to place the shelves onto and didn't go with a more permanent solution.

I did however, want an intentional solution as some of the higher shelves would be seen from the underside. The rails are hidden from view along with the mounting hardware and the support structure itself is shaped like crown molding. I used PLA for the support and PLA tough for the rails. I'm sure one could get away with PETG for the rails as well.

Assembly:
Install rails, they're countersunk with some flexibility
Slide Back support on
Slide side supports on
install shelf on top.