I put together a quick template to create some 3×5 iniative cards to upgrade my colored index cards with sharpie. You can find the word document here. Copy whichever blank template you want enough times to create enough cards. One is a blank 3×5 card that folds in half. The other style has a space on each side for some statistics. Then, drop your chosen images into the blank spaces, then resize and crop the images until they fit inside the template. Flip one image of the folded card so that both images face up when folded.
Above, I printed mine, cut them out, glued them to index cards, and then trimmed off any overhang.
I ran across this imgur gallery of collected and stylized natural environments. It seems especially useful for anyone using a digital platform for their games, but even tabletop gamers might want something to print off or show from their phone.
Hack and Slash Master has an excellent house rule for creating, designing, and running ships and vehicles of all sorts. http://hackslashmaster.blogspot.com/2017/01/on-ship-design.html I can see this same system being a good starting point to make a similar minimalist system for fortresses, dungeons, and complexes that players are inevitably interested in building, refurbishing, or stealing.
Here are two more of the riddles included in my latest dmsguild product release, priced at $9.87. Including a guide to riddle and puzzle creation plus 40 puzzles, you are paying $0.25 per puzzle.