Rocky terrain, which is difficult enough to walk on that you must go around it or levitate or fly over it, but permits magic and items to pass over it.

An option that causes the game to show you a test screen before going into character selection options. This test screen should have your default terminal background and show monsters of every possible color, so you can see if any particular color is unreadable on the background (dark blue and dark gray are common culprits for this) and adjust your settings as necessary.