Mima Mounds Natural Area Preserve is an interesting mystery.  No one seems to know how these mounds were created.  They are not burial mounds of any kind.  The most widely accepted theory is that these were created river currents from the melting during the Ice Age.

Walking through these is like being in a maze.  It is easy to disappear because many are several feet high.

There's thousands of these mounds as far as you can see.