Honeycombs are actively built by bees, the bees could make just about any shape but over a long period of natural selection their behavior evolved to make shapes that minimize the area of wax needed and still be structurally functional for their needs. Perhaps the same structural principles could be used when trying to improve concrete casting and reducing the amount of material needed to make a variety of concrete shapes.
Image source: https://www.quora.com/Why-does-nature-prefer-hexagonal-shapes
Meanders are sinuous bends in a river with a faster flow of water on the outside channel leaving the inside to be slower therefore depositing sediments. The water flows faster on the outside bend of a river because it has further to travel, its speed and erosive power is therefore greater. This erodes the outside of the meander, producing a river cliff and deeper channel on that side. The bends become deeper and deeper in time, until the water finds a shortcut and the bends are cut off, drying out or becomes separate lakes.
Image source: https://sites.google.com/site/stmarysfluvialstudies/meanders-alice-emily
Found throughout the Big Island of Hawaii, lava tubes and caves are perfect examples of how nature forms itself. Lava caves like the one in the picture above are formed when a river of lava gradually builds solid walls and a ceiling as it is flowing. When the lava flow stops and the last of it passes downhill and into the ocean, a tube/cave is left. These caves can be a few feet high and only yards long, or they can stretch for miles with high ceilings.
Having explored some of these myself, I find it fascinating how the lava cools around itself and forms these kind of gravity defying spaces that create networks of tunnels under the surface of the islands.