A simple printable paper lantern. Just drop any battery powered tea light in and have a pleasantly glowing cube, and if you want it to look fancier paint the top and bottom edges gold.

My set was printed out of glow in the dark PLA, and have technically survived about a year on the patio... But do look worse for it. The walls should end up 2 layers thick and allow for light to glow through if you are using a white or translucent filament.

If you do leave them outside, drill a couple holes in the bottom to allow water to drain, and weigh them down with rocks so they don't blow around to much.