16. The lightning.
Traditionally, 16 is the tower card in the Rider-Waite tarot deck, but in the older _belgian_ variant it was still called "La Foudre", meaning the lightning strike. As I am a Belgian, born and raised, I decided to re-de-imagine the card back as it's original version, and depicted it without a tower.
Instead I went for a solitary tree, struck by lightning.
I think it works quite well visually, and links nicely together with other cards with similar visual elements. Like the tree in the Hanged man card. I also think I'll go back to the lovers to make the background design more in line with this one.

08/12/2021: Updated the lightning strike itself, made it more jagged and cleaner.

Edit 01/12/2023:
Updated to black/white/gold version, only very minor tweaks needed.
Kept the lightning white to maintain contrast, turned the starchart in the back gold instead